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MOLYBDENUM, FERROMOLYBDENUM, AND AMMONIUM MOLYBDATE

A. Commodity Summary

Almost all molybdenum is recovered from low-grade deposits of the mineral molybdenite, naturally occurring molybdenum disulfide (MoS2), mined either from a primary deposit, or as a byproduct of copper processing.1 In 1993, one mine extracted molybdenum ore, and nine mines recovered molybdenum as a byproduct. Two plants converted molybdenite concentrate to molybdic oxide, which was used to produced ferromolybdenum, metal powder, and other molybdenum compounds.2 Exhibit 1 presents the names and locations of molybdenum mines and processing facilities.

EXHIBIT 1

SUMMARY OF MOLYBDENUM, MOLYBDIC OXIDE, AND FERROMOLYBDENUM PRODUCERSa

Facility Name Location

Cyprus-Climax - Henderson

Cyprus-Climax

Cyprus-Climax

Cyprus-Climax - Green Valley

Cyprus-Climax

Kennecott

Molycorp Inc.

Montana Resources Inc.

Phelps Dodge

San Manuel

San Manuel

Thompson Creek

Thompson Creek

Empire, CO

Fort Madison, IA

Clear Water, MI

Tucson, AZ

AZ

Bingham Canyon, UT

Washington, PA

Butte, MT

Chino, NM

San Manuel, AZ

Morenci, AZ

Chalis, ID

Langeloth, PA

Baghdad,

a - Personal Communication between ICF Incorporated and John W. Blossom, U.S. Bureau of Mines, October 1994.

Molybdenum metal is a refractory metal used as an alloying agent in steels, cast irons, and superalloys.3

Ferromolybdenum is an alloy of iron and molybdenum used primarily as an alternative additive in producing alloy steels, cast irons, and nonferrous alloys. The two most common grades of ferromolybdenum are low carbon- and high carbon ferromolybdenum. Ammonium molybdate is an intermediate in manufacturing both molybdenum metal and molybdic oxide, although it can also be sold as a product. Purified MoS2 concentrate also is used as a lubricant.

1 J.W. Blossom, "Molybdenum," from Minerals Yearbook Volume 1. Metals and Minerals, U.S. Bureau of Mines, 1992, p. 849.

2 J.W. Blossom, "Molybdenum," Mineral Commodity Summaries, U.S. Bureau of Mines, January 1995, p. 114.

3 J.W. Blossom, 1992, Op. Cit., p. 847.

B. Generalized Process Description

1. Discussion of Typical Production Processes

Molybdenum and molybdenum products, including ammonium molybdate, are made by roasting concentrated ore, followed by purification and/or reduction. Ferromolybdenum is typically produced by reaction of technical grade molybdic oxide and iron oxide with a conventional metallothermic process using silicon and/or aluminum as the reductant. These processes are described in greater detail below.

2. Generalized Process Flow Diagram

Molybdenum Metal and Ammonium Molybdate

Molybdenum metal and ammonium molybdate are made by roasting concentrated molybdenite ore, as shown in Exhibit 2. The concentration operations, which are not shown, include crushing, grinding, and flotation of either primary or copper ores. Molybdenite is recovered from either primary molybdenite or copper sulfide ore by flotation, after the ore has been crushed and ground to a suitable size. Several stages of grinding and reflotation concentrate the molybdenite in the primary ore to a 90 to 95 percent purity concentrate.4 The remainder of the concentrate is primarily silica.5 Copper, iron and lead are the impurities removed as tailings by this flotation process. Several sequential stages of flotation also are used for the copper ore, first to separate the gangue, and then the copper. The molybdenite concentration is usually 70 to 90 percent purity, when recovered from copper ores.6

Technical grade molybdic oxide, consisting of 90 to 95 percent MoO3, is produced by roasting molybdenite concentrate in a multiple hearth furnace at temperatures up to 650°C.7 Molybdenum concentrates may be leached with nitric acid prior to roasting to reduce the alkali concentrations in the concentrates.8 The roasting process removes sulfur and converts the sulfide to oxide. The flue gas contains products of combustion, SO2, and may contain rhenium or selenium. The SO2 in the flue gas is converted to sulfuric acid (H2SO4).9 More information on the processing of the flue gas, and the production of sulfuric acid can be found in the Rhenium and Selenium sections of this document.

Pure molybdic oxide can be produced from technical grade molybdic oxide through sublimation and condensation or by leaching. In sublimation, the technical grade oxide is heated to approximately 1,100°C in a muffle type furnace. The oxide is vaporized and carried in a stream of forced air through cooling ducts and

4 Ibid., p. 850.

5 "Molybdenum and Molybdenum Alloys," from Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Vol. XV, 1981, p. 670.

6 Blossom, J. W., 1992, Op. Cit., p. 850.

7 Ibid., p. 848.

8 U.S. Environmental Protection Agency, Development Document for Effluent Limitations Guidelines and Standards for the Nonferrous Metals Manufacturing Point Source Category, Volume VI, Office of Water Regulations and Standards, May 1989, p. 3364.

9 "Molybdenum and Molybdenum Alloys," 1981, Op. Cit., p. 670.

EXHIBIT 2

MOLYBDENUM PRODUCTION Gas

(Source: Development Document for Effluent Limitations Guidelines, 1989, p. 3370.)

SO2 Scrubber or Acid Plant

Rhenium Recovery Scrubber

Roasting

Leaching

Wastewater

Gas

Wastewater

Technical Grade Molybdic Oxide

Sublimation

Leaching

Acid Water

Pure Molybdic Oxide Reduction

Furnace

Pure Molybdic Oxide

Scrubber

Wastewater

Dissolution, Crystallization Calcining

AmmoniumMolybdate

Ammonium Molybdate

H2 Gas

Molybdenum MetalPowder

Solvent Extraction or Ion Exchange

Wastewater

Molybdenum Sulfide

Dissolving, Crystallization

Crude Ammonium Perrhenate

Concentrate

Molybdenum Sulfide

Purification, Reduction

Concentrate

Rhenium Meta

Pure Pure Molybdic

NH4OH Water Ammonium Molybdic

Wastewater Oxide Molybdate Oxide

the condensed oxide particles are collected in a fabric filter. The purified oxide contains greater than 99.5 percent MoO3. Technical grade oxide may also be purified by leaching with a hydrochloric acid-ammonium chloride solution (not shown). The impurities are dissolved and separated from the solid molybdic oxide by filtration. The pure oxide may be sold as a product, reduced to molybdenum metal powder, or used to produce various molybdenum chemicals.10

Ammonium molybdate is formed by reacting technical grade molybdic oxide with ammonium hydroxide and crystallizing out the pure molybdate. The ammonium molybdate may be sold as product, calcined to form pure molybdic oxide, or reduced to form molybdenum metal powder.11

Hydrogen is used to reduce ammonium molybdate or pure molybdic oxide to molybdenum powder, at 500-1150°C, in a boat- or tube-type furnace. The metal powder is sintered and cast into ingots or bars.12

Ferromolybdenum

Exhibit 3 illustrates the production of low carbon and high carbon ferromolybdenum. Low carbon ferromolybdenum is produced by mixing technical grade molybdic oxide, aluminum, ferrosilicon, iron oxide, limestone, lime, and fluorspar, and igniting the aluminum (not shown). A metal button and a slag are formed, allowed to solidify, and then are separated.13 One firm added that when it produces low carbon ferromolybdenum no furnace is necessary, only a sand bed.14 High carbon content ferromolybdenum is made by reducing technical grade molybdic oxide, calcium molybdate, or sodium molybdate with carbon in the presence of iron in an electric furnace (not shown). The impurities from a slag which is discarded.15 Low carbon ferromolybdenum produced by the thermite process is more common than the high carbon alloy.

3. Identification of Novel or Distinct Processes

One researcher has investigated the separation and recovery of critical metals (including molybdenum) from mixed and contaminated superalloy scrap.16

10 U.S. Environmental Protection Agency, 1989, Op. Cit., p. 3364.

11 Ibid.

12 "Molybdenum and Molybdenum Alloys," 1981, Op. Cit., p. 674.

13 U.S. Environmental Protection Agency, "Molybdenum," 1988 Final Draft Summary Report of Mineral Industrial Processing Wastes, 1988, p. 3-154.

14 Molycorp, Inc. Comment submitted in response to the Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes. January 25, 1996.

15 Ibid., p. 3-154.

16 Hundley, G.L., and D.L. Davis, "Recovery of Critical Metals from Superalloy Scrap by Matte Smelting and Hydrometallurgical Processing," U.S. Bureau of Mines Report of Investigations 9390, 1991, p. 1.

EXHIBIT 3

FERROMOLYBDENUM PRODUCTION

Aluminum, Technical Grade Molybdic Oxide, Ferrosilicon, Iron Oxide, Limestone, Lime and Fluorspar

Furnace Slag

Low Carbon Ferromolybdenum

Technical Grade Oxide, Iron, Calcium or Sodium Molybdate, Carbon

Furnace Slag

High Carbon Ferromolybdenum

4. Extraction/Beneficiation Boundaries

EPA established the criteria for determining which wastes arising from the various mineral production sectors come from mineral processing operations and which are from beneficiation activities in the September 1989 final rule (see 54 Fed. Reg. 36592, 36616 codified at 261.4(b)(7)). In essence, beneficiation operations typically serve to separate and concentrate the mineral values from waste material, remove impurities, or prepare the ore for further refinement. Beneficiation activities generally do not change the mineral values themselves other than by reducing (e.g., crushing or grinding), or enlarging (e.g., pelletizing or briquetting) particle size to facilitate processing. A chemical change in the mineral value does not typically occur in beneficiation.

Mineral processing operations, in contrast, generally follow beneficiation and serve to change the concentrated mineral value into a more useful chemical form. This is often done by using heat (e.g., smelting) or chemical reactions (e.g., acid digestion, chlorination) to change the chemical composition of the mineral. In contrast to beneficiation operations, processing activities often destroy the physical and chemical structure of the incoming ore or mineral feedstock such that the materials leaving the operation do not closely resemble those that entered the operation. Typically, beneficiation wastes are earthen in character, whereas mineral processing wastes are derived from melting or chemical changes. The idea that beneficiation wastes are earthen in character is only a guide, and not a standard. There may be instances where beneficiation operations produce a waste that is “not” earthen in character. In such instances, the operation is not considered a processing operation, because of the waste’s non-earthen characteristics, and instead remains a beneficiation operation.

EPA approached the problem of determining which operations are beneficiation and which (if any) are processing in a step-wise fashion, beginning with relatively straightforward questions and proceeding into more detailed examination of unit operations, as necessary. To locate the beneficiation/processing "line" at a given facility within this mineral commodity sector, EPA reviewed the detailed process flow diagram(s), as well as information on ore type(s), the functional importance of each step in the production sequence, and waste generation points and quantities presented above.

Molybdenum Powder

EPA determined that for the production of molybdenum powder, the beneficiation/processing line occurs between the roasting and sublimation steps because leaching does not follow and because the molybdenum disulfide is chemically roasted to pure molybdic oxide.17 Therefore, because EPA has determined that all operations following the initial "processing" step in the production sequence are also considered processing operations, irrespective of whether they involve only techniques otherwise defined as beneficiation, all solid wastes arising from any such operation(s) after the initial mineral processing operation are considered mineral processing wastes, rather than beneficiation wastes. EPA presents below the mineral processing waste streams generated after the beneficiation/processing line, along with associated information on waste generation rates, characteristics, and management practices for each of these waste streams.

Ammonium Molybdate and Pure Molybdic Oxide

Based on a review of the process, there are no mineral processing operations involved in the production of either ammonium molybdate or pure molybdic oxide.

Ferromolybdenum

EPA determined that for ferromolybdenum, the beneficiation/processing line occurs at the furnace where the technical grade molybdic oxide and other materials are charged and undergo thermal reduction to form

17 Molycorp, Inc. Op. Cit.

ferromolybdenum. One firm, Molycorp Inc., reported that in their operations furnaces were restricted to high carbon ferromolybdenum production.18

C. Process Waste Streams

1. Extraction/Beneficiation Wastes

The following wastes may be generated by extraction and beneficiation operations: gangue, flotation tailings, spent flotation reagents, and wastewater.19,20 The tailings from molybdenite concentration are not expected to exhibit any hazardous characteristics, although metal leaching and acid formation may take place.21

2. Mineral Processing Wastes

Ammonium Molybdate Refining

Refining Wastes. Available data do not indicate that ammonium molybdate refining wastes exhibit any hazardous characteristics.22 Therefore, the Agency did not evaluate this material further.

Technical Grade Molybdic Oxide Production

Liquid Residues. Approximately 1,000 metric tons of liquid residues are generated annually in the United States. Available data indicate that this waste is potentially TC toxic. Potentially hazardous constituents include arsenic, cadmium, lead, and selenium.23 The waste is not recycled. Liquids from the quench and scrubber towers/thickener contained the following constituents: arsenic - 60 ppm; cadmium - 1.2 ppm; chromium - 1.8 ppm; lead - 5.8 ppm; molybdenum - 100 ppm; and selenium - 32 ppm.24 Additional data is provided in Attachment 1. No other information on waste characteristics, or waste management was available in the sources listed in the bibliography.

Treatment Solids. Available data do not indicate that treatment solids exhibit any hazardous characteristics.25 Silicon was found at a concentration of 10 percent in solids from the quench and scrubber towers/thickener.26 Therefore, the Agency did not evaluate this material further.

18 Ibid.

19 PEI Associates, Site Specific Data Summary Forms: Facilities Involved in the Extraction and Beneficiation of Ores and Minerals, Prepared for U.S. Environmental Protection Agency, Office of Research and Development, November 1986.

20 Weiss, Norman L., Ed. "Molybdenum," SME Mineral Processing Handbook, Volume II, Society of Mining Engineers, 1985, pp. 16-1 - 16-36.

21 U.S. Environmental Protection Agency, 1988, Op. Cit., p. 3-152.

22 U.S. Environmental Protection Agency, Newly Identified Mineral Processing Waste Characterization Data Set, Volume I, Office of Solid Waste, August 1992, p. I-2.

23 Ibid., p. I-6.

24 Ibid., Vol. II, p. 28-11.

25 Ibid., Vol. I, p. I-6.

26 Ibid., Vol. II, p. 28-8.

Solid Residues. Available data do not indicate that solid residues exhibit any hazardous characteristics (see Attachment 1).27 Therefore, the Agency did not evaluate this material further.

Roaster Gas Blowdown Solids. Approximately 100 metric tons of roaster gas blowdown solids are generated annually in the United States. Available data do not indicate that this waste exhibits any hazardous characteristics.28 Therefore, the Agency did not evaluate this material further.

Molybdic Oxide Refining Wastes. Approximately 2,000 metric tons of molybdic oxide refining wastes are generated annually in the United States.29 This waste is believed to not exhibit any hazardous characteristics30

and has not been evaluated further by the Agency.

Flue Dust/Gases. The flue gases produced during the roasting of molybdenite concentrates could contain volatile metals in the flue dust, in addition to the SO2. These metals may include lead, zinc, tin and others.31

Although no published information regarding waste generation rate was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 1,100 metric tons/yr, 250,000 metric tons/yr, and 500,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristic of toxicity for lead. This waste typically is not recycled. However, Molycorp Inc. reported that flue dust is recycled at its Washington, PA facility. It also reported that in its operations there was no difference between flue dust/gases and roaster gas blowdown solids.32

Metal Refining

Refining Wastes. Available data do not indicate that metal refining wastes exhibit any hazardous characteristics.33 Therefore, the Agency did not evaluate this material further.

H2 Reduction Furnace Scrubber Water. Existing data and engineering judgment suggest that this material does not exhibit any characteristics of hazardous waste (see Attachment 1). Therefore, the Agency did not evaluate this material further.

Ferromolybdenum Production

APC Dust/Sludge. This waste is generated by the baghouse or other APC device receiving the fumes from the ferromolybdenum furnace. Available data do not indicate that APC dust/sludge exhibits any hazardous characteristics.34 Therefore, the Agency did not evaluate this material further.

27 Ibid., Vol. II, p. I-6.

28 Ibid.

29 Ibid.




33 U.S. Environmental Protection Agency, 1992, Op. Cit, Vol. I, p. I-6.

34 Ibid., p. I-4.

Slag. This waste, formed in either the production of low carbon ferromolybdenum or high carbon ferromolybdenum, is not expected to exhibit any hazardous characteristics. The slag is usually discarded.35

Therefore, the Agency did not evaluate this material further.

D. Non-uniquely Associated Hazardous Wastes

Ancillary hazardous wastes may be generated at on-site laboratories, and may include used chemicals and liquid samples. Other hazardous wastes may include spent solvents, and tank cleaning wastes. Non-hazardous wastes may include tires from trucks and large machinery, sanitary sewage, and waste oil and other lubricants.

E. Summary of Comments Received by EPA

New Factual Information

Two commenters provided new information on facility specific operations and processes (COMM40, COMM69). This new information has been incorporated into the Agency’s sector report.

Site-specific Issues

None.


BIBLIOGRAPHY

Blossom, J. W. "Molybdenum." From Mineral Commodity Summaries. U.S. Bureau of Mines. January 1995. pp. 114-115.

Blossom, J. W. "Molybdenum." From Mineral Facts and Problems. U.S. Bureau of Mines. 1985. pp. 521-534.

Blossom, J. W. "Molybdenum." From Minerals Yearbook Volume 1. Metals and Minerals. U.S. Bureau of Mines. 1992. pp. 847-862.

Hundley, G.L., and D.L. Davis. "Recovery of Critical Metals from Superalloy Scrap by Matte Smelting and Hydrometallurgical Processing." From Report of Investigations 9390. U.S. Bureau of Mines. 1991. pp. 1-11.

ICF Incorporated. Amax Incorporated, Fort Madison, IA: Mineral Processing Waste Sampling Visit — Trip Report. August 1989.

ICF Incorporated. Magma Copper Company, San Manuel, AZ: Mineral Processing Waste Sampling Visit — Trip Report. August 1989.

"Manganese." From An Appraisal of Minerals Availability for 34 Commodities. U.S. Bureau of Mines. 1987. pp. 191-199.

"Molybdenum and Molybdenum Alloys." Kirk-Othmer Encyclopedia of Chemical Technology. Vol. XV. 3rd ed., 1981. pp. 670-690.

PEI Associates. Site Specific Data Summary Forms: Facilities Involved in the Extraction and Beneficiation of Ores and Minerals. Prepared for U.S. Environmental Protection Agency, Office of Research and Development. November 1986.

Personal Communication between ICF Incorporated and John W. Blossom, U.S. Bureau of Mines. October 1994.

RTI Survey 100214. National Survey of Solid Wastes From Mineral Processing Facilities. Climax Molybdenum Company, Fort Madison, IA. 1989.

RTI Survey 102145. National Survey of Solid Wastes From Mineral Processing Facilities. Molycorp, Inc., Washington, PA. 1989.

U.S. Environmental Protection Agency. Development Document for Effluent Limitations Guidelines and Standards for the Nonferrous Metals Manufacturing Point Source Category. Volume VI. Office of Water Regulations and Standards. May 1989.

U.S. Environmental Protection Agency. "Molybdenum." From 1988 Final Draft Summary Report of Mineral Industrial Processing Wastes. 1988. pp. 3-152 - 3-157.

U.S. Environmental Protection Agency. Newly Identified Mineral Processing Waste Characterization Data Set. Office of Solid Waste. August 1992.

U.S. Environmental Protection Agency. Technical background Document, Development of Cost, Economic, and Small Business Impacts Arising from the Reinterpretation of the Bevill Exclusion for Mineral Processing Wastes. August 1989. pp. 3-5 - 3-6.

Weiss, Norman L., Ed. "Molybdenum." SME Mineral Processing Handbook. Vol. II. Society of Mining Engineers. 1985. pp. 16-1 - 16-36.

ATTACHMENT 1

SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - SOLID RESIDUES - MOLYBDENUM OXIDE

Constituents Total Constituent Analysis - PPM

Minimum Average Maximum # Detects EP Toxicity Analysis - PPM TC # Values

Minimum Average Maximum # Detects Level In Excess Aluminum Antimony Arsenic Barium Beryllium Boron Cadmium Chromium Cobalt Copper Iron Lead Magnesium Manganese Mercury Molybdenum Nickel Selenium Silver Thallium Vanadium Zinc Cyanide Sulfide Sulfate Fluoride Phosphate Silica Chloride TSS pH * Organics (TOC)

- - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

100,000 100,000 100,000 1/1 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 100.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 0.2 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 0 - -

Non-detects were assumed to be present at 1/2 the detection limit. TCLP data are currently unavailable; therefore, only EP data are presented.

SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - H2 REDUCTION FURNACE SCRUBBER WATER - MOLYBDENUM OXIDE




- - - 0/0 0.001 0.0090 0.024 3/3 0.002 0.0107 0.024 3/3

- - - 0/0 0.001 0.0023 0.005 3/3

- - - 0/0 0.001 0.0010 0.001 3/3 0.001 0.0040 0.006 3/3

- - - 0/0 0.004 0.3947 0.64 3/3

- - - 0/0 0.001 0.0657 0.17 3/3

- - - 0/0 - - - 0/0

0.0002 0.0002 0.0002 3/3 - - - 0/0

0.024 1.1613 2.8 3/3 0.001 0.0010 0.001 3/3 0.001 0.0053 0.014 3/3 0.001 0.0010 0.001 3/3

- - - 0/0 0.51 0.5733 0.63 3/3 0.01 0.0100 0.01 3/3

- - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 100.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 0.2 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 0 - -


PHOSPHORIC ACID


Most phosphoric acid facilities are co-located with other manufacturing facilities.1 The primary product from phosphoric acid facilities is commercial-grade wet process phosphoric acid, approximately 95 percent of which is used at co-located facilities to produce fertilizers and animal feed. Most of the remaining portion is used as a feedstock in chemical processing operations. Phosphoric acid producing facilities are listed in Exhibit 1.

EXHIBIT 1

SUMMARY OF PHOSPHORIC ACID PRODUCING FACILITIES

Facility Name Locations Type of Operations

Potential Factors Related to Sensitive Environments

Agrico Chem Pierce, FL Uncle Sam, LA Donaldsonville, LA

Wet Process Wet Process Wet Process

Uncertain Uncertain Uncertain

Albright & Wilson Fernald, OH Charleston, SC

Furnace Furnace

Uncertain Uncertain

Arcadian Geismar, LA Wet Process Located in 100-year floodplain, within 1 mile of wetland

Cargill Riverview (Tampa), FL Wet Process Located in 100-year floodplain, located in wetland

Central Phosphates Plant City, FL Wet Process Within 1 mile of wetland, located in area of karst terrain

CF Ind. Bartow, FL Wet Process Uncertain

Chevron Rock Springs, WY Wet Process Uncertain

Conserv Nichols, FL Wet Process Within 1 mile of wetland

Farmland Pierce (Bartow), FL Wet Process Within 1 mile of wetland

FMC Carteret, NJ Lawrence, KS Newark, CA

Furnace Furnace Furnace

Uncertain Uncertain Uncertain

Gardinier, Inc. Riverview, FL Wet Process Uncertain

Hydrate Milwaukee, WI Furnace Uncertain

IMC Mulberry, FL Wet Process Located within 1 mile of wetland

1 U.S. Environmental Protection Agency, "Phosphoric Acid Production," from Report to Congress on Special Wastes from Mineral Processing, Vol. II, Office of Solid Waste, July 1990, pp. 12-1 - 12-61.

EXHIBIT 1 (continued)

Facility Name Locations Type of Operations

Potential Factors Related to Sensitive Environments

JR Simplot Pocatello, ID Wet Process Located in 100-year floodplain, located in fault zone

Mobil Pasadena, TX Wet Process Located in 100-year floodplain

Monsanto Trenton, MI Augusta, GA Carondelet, MO Long Beach, CA

Furnace Furnace Furnace Furnace

Uncertain Uncertain Uncertain Uncertain

Nu West Soda Springs (Conda), ID Wet Process Uncertain

Nu South Pascagoula, MS Wet Process

Occidental Jeffersonville, IN Columbia, TN White Springs, FL

Dallas, TX

Furnace Furnace Wet Process

Furnace

Uncertain Uncertain Located within 1 mile of wetland Uncertain

Royster Palmetto (Piney Pt.), FL

Mulberry, FL

Wet Process

Wet Process

Located within 6.5 miles of endangered species habitat, within 1 mile of wetland, located in area of karst terrain

Located within 1 mile of wetland

Seminole Bartow, FL Wet Process Located in endangered species habitat, located in 100-year floodplain, within 1 mile of wetland

Stauffer Morrisville, PA Nashville, TN Richmond, CA Chicago Heights, IL Chicago, IL

Furnace Furnace Furnace Furnace Furnace

Uncertain Uncertain Uncertain Uncertain Uncertain

Texasgulf Aurora, NC Wet Process Located in 100-year floodplain, located in wetland

US Agri-Chemicals Corp (USAC)

Ft. Meade, FL Wet Process Within 1 mile of wetland Uncertain


There are two processes for producing phosphoric acid: (1) the wet process, and (2) the furnace process. Wet process acid, produced directly from phosphatic ores, is characterized by relatively high production volume, low cost, and low purity. It is used primarily in fertilizers. Furnace or thermal acid, manufactured from elemental phosphorus, is more expensive and considerably purer than wet-process acid. It also is produced in much smaller quantities, almost exclusively for applications requiring high purity.2 As shown in Exhibit 1, there are 22 facilities that use the wet process and 18 that use the furnace process. There are significant differences in these processes and therefore, this report is divided into two sections. The wet process, as described in Section 1, is the main focus of this chapter. A brief discussion of the furnace process is provided in Section 2. (The furnace process uses a saleable mineral commodity as a primary raw material (element al phosphorous) and as such, is completely outside the scope of the Mining Waste Exclusion.) Finally, Section 3 describes several related processes such as ammoniated fertilizer production, animal feed production, superphosphoric acid production, fluoride recovery, and sulfuric acid production.

SECTION 1: The Wet Process

1. Discussion of the Typical Production Processes

Wet process steps include digestion, filtration, and concentration. Phosphate rock is dissolved in phosphoric acid, to which sulfuric acid is added. The slurry from this operation is sent to filters where solids are collected, washed, and sent to phosphogypsum stacks. The acid is concentrated by evaporation. The wet process is described in more detail below.


During digestion, the first step in phosphoric acid production, beneficiated phosphate rock is dissolved in phosphoric acid; sulfuric acid, which chemically digests the calcium phosphate, is added to this solution. The product of this operation is a slurry that consists of the phosphoric acid solution and a suspended solid, calcium sulfate, commonly known as phosphogypsum. The slurry is routed to a filtration operation where the suspended phosphogypsum is separated from the acid solution. The acid isolated during filtration is concentrated through evaporation to produce "merchant grade" (54 percent) phosphoric acid. The phosphogypsum is re-slurried, this time in recycled process wastewater, and sent to disposal in phosphogypsum stacks.3 Exhibit 2 presents a process flow diagram of phosphoric acid production.4

Only five percent of raw product acid is purified. Purification of wet-process acid is accomplished by two primary methods: (1) solvent extraction, and (2) chemical precipitation. Exhibit 3 presents a typical flow diagram for solvent extraction purification of wet-process phosphoric acid. (Purification steps are outside the scope of mineral processing.) In the production of sodium phosphates using chemical precipitation, almost all wet-process acid impurities may be induced to precipitate as the acid is neutralized with sodium carbonate or sodium hydroxide. The main exception, sulfate, may be precipitated as calcium or barium sulfate. Most fluorine and silica can be removed with the sulfate filter cake as sodium fluorosilicate by the addition of sodium ion and control of the Si/F ratio in the process.5

2 "Phosphoric Acid and the Phosphides," Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., Vol. XVII, 1982, pp. 426-442.

3 U.S. Environmental Protection Agency, 1990, Op. Cit., pp. 12-1 - 12-61.

4 Ibid.

5 Kirk-Othmer Encyclopedia of Chemical Technology, 1982, Op. Cit., pp. 426-442.

EXHIBIT 2

PHOSPHORIC ACID TREATMENT

(Adapted from: Report to Congress on Special Wastes from Mineral Processing, July 1990, pp. 12-1 - 12-61.)

Process Special Waste Management

Beneficiated Phosphate

Sulfuric Acid Rock (BPR)

Phosphoric Acid Production

Digestion

Filtration

Uranium Extraction (Optional)

Defluorination (Options)

Concentration

Super Phosphate

Acid Production (Optional)

Non-Ammoniated Animal Feed (Optional)

Process Wastewater Phosphogypsum

Process Wastewater

Process Wastewater

Process Wastewater

Gypsum Stack

Storage Surface

Impoundment

Return to

Production

NPDES Discharge

Hydrofluosilicic Acid (Optional)

BPR Phosphoric

Acid

Super Phosphoric

Acid

Animal Feed

BPR Limestone and/or Soda Ash

Merchant Grade Phosphoric Acid Production Operation

Special Waste

Waste Management Unit

EXHIBIT 3

SOLVENT EXTRACTION PURIFICATION OF WET PROCESS PHOSPHORIC ACID

(Adapted from: Kirk-Othmer Encyclopedia of Chemical Technology, 1982, pp. 426 - 442.)

Solvent

Wet Process

Extraction Backwash Acid

Release

Solvent Recovery

Solvent Recovery

H2O Acid

Depleted Raffinate Raffinate

Stripping

Concentration and

Defluorination

Fertilizer Product

In the double-neutralization process for wet process acid purification, sodium fluorosilicate is precipitated and removed by filtration at a pH of 3-4. Upon raising the pH to 7-9, insoluble phosphates of iron, aluminum, calcium, and magnesium form and separate. Iron can be precipitated as hydrous ferric oxide, reducing the phosphate loss in the second filter cake. Both the fluorosilicate and metal phosphate filter residues tend to be voluminous cakes that shrink when dewatered; recovery of soluble phosphates trapped within the cakes is difficult.6

The double-neutralization process is used in the production of high volume detergent-builder phosphates because the phosphate precursor solutions occur at pH 7-9. More acidic salts, however, require an additional filtration to eliminate discoloration caused by remaining traces of ferric oxide that precipitate at higher pH.7

The increasing cost differential between the sulfur used in manufacture of wet-process acid and the electricity needed for thermal acid has encouraged the development of new processes for purifying wet-process acid. These are based mostly on solvent extraction using organic solvents with low miscibility in water. Crude wet-process acid is typically concentrated and clarified prior to extraction to remove sludge-forming components and improve partition coefficients. Chemical precipitation of sulfate, silicate, and fluoride may also be used as a prepurification step preceding solvent extraction.8

Organic-phase extraction of H3PO4 is accomplished in a series of countercurrent mixer-settlers, with extraction generally limited to 50-75 percent of the feed acid P2O5 content. Higher extraction results in sludge precipitation in the settlers and in the depleted raffinate stream. Raffinate is stripped of residual solvent and used in fertilizer production.9

The acid is washed from the organic stream by water or aqueous alkali in another series of countercurrent mixer-settlers, stripped of residual solvent, and concentrated to the desired P2O5 level. The solvent is recycled to the extraction section. Many variations of this basic scheme have been developed to improve extraction of phosphate and rejection of impurities to the raffinate stream, and numerous patents have been granted on solvent extraction processes.10

Processing phosphate rock to produce phosphate fertilizer is water-intensive. At larger wet process phosphoric acid plants, water use can reach 50,000 gallons per ton of phosphoric acid. At one phosphoric acid plant with a rated capacity of 4,500 tons per day, 155,000 gallons of water per minute are used. Water uses include phosphogypsum transport, phosphoric acid concentration, and phosphoric acid temperature control and cooling.11

3. Identification/Discussion of Novel (or otherwise distinct) Processes

None identified.

6 Ibid.

7 Ibid.

8 Ibid.

9 Ibid.

10 Ibid.

11 The Fertilizer Institute. Comment submitted in response to the Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes. January 25, 1995.

4. Beneficiation/Processing Boundaries


Mineral processing operations, in contrast, generally follow beneficiation and serve to change the concentrated mineral value into a more useful chemical form. This is often done by using heat (e.g., smelting) or chemical reactions (e.g., acid digestion, chlorination) to change the chemical composition of the mineral. In contrast to beneficiation operations, processing activities often destroy the physical and chemical structure of the incoming ore or mineral feedstock such that the materials leaving the operation do not closely resemble those that entered the operation. Typically, beneficiation wastes are earthen in character, whereas mineral processing wastes are derived from melting or chemical changes.


EPA determined that for the production of phosphoric acid via the wet process, the beneficiation/ processing line occurs between beneficiation of phosphate rock and digestion, because the beneficiated phosphate rock undergoes a complete acid digestion, which destroys the physical matrix of the rock to yield phosphoric acid and phosphogypsum. Therefore, because EPA has determined that all operations following the initial "processing" step in the production sequence are also considered processing operations, irrespective of whether they involve only techniques otherwise defined as beneficiation, all solid wastes arising from any such operation(s) after the initial mineral processing operation are considered mineral processing wastes, rather than beneficiation wastes. EPA presents below the mineral processing waste streams generated after the beneficiation/processing line, along with associated information on waste generation rates, characteristics, and management practices for each of these waste streams.

SECTION 2: The Furnace Process

1. Discussion of the Typical Production Processes

In the furnace process, elemental phosphorus is burned to phosphorus pentoxide which is sent to hydration for the production of phosphoric acid. This entire operation uses a saleable mineral commodity as a primary raw material (elemental phosphorus) and therefore is completely outside the scope of the Mining Waste Exclusion.


In the manufacture of phosphoric acid from elemental phosphorus, phosphorus is burned in excess air, the resulting phosphorus pentoxide is hydrated, the heats of combustion and hydration are removed, and the phosphoric acid mist is collected. There are three principal process unit types used to deal with the very high combustion-zone temperatures, the reactivity of hot phosphorus pentoxide, the corrosive nature of hot phosphoric acid, and the difficulty of collecting the very fine phosphoric acid mist. These process unit types are (1) wetted wall, (2) water-

cooled, and (3) air-cooled; depending on the method used to protect the combustion chamber wall.12 Exhibit 4 presents process flow diagrams for the three furnace-grade phosphoric acid production process units.

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphorus is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air supplied by a forced or induced draft fan. Acid sprays at either the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphorus pentoxide.13

When all the acid is to be converted into sodium phosphate salt, a variation of the wetted-wall acid plant is used. In this case, a relatively noncorrosive, neutral sodium phosphate solution is circulated in lieu of phosphoric acid. Phosphorus pentoxide absorption is rapid and over 95 percent is collected by the circulating stream. Alkali and make-up water are added through a tail scrubber as dilute caustic soda, soda ash, or sodium sesquicarbonate solution adjusted to maintain the system materials balance.14

Air-cooled plants are characterized by a large refractory-lined combustion chamber from which waste heat is removed by radiation and convection. The combustion chamber is constructed of carbon steel lined with a single layer of high alumina refractory brick.15

Hot combustion gases from both the air-cooled combustion chamber and the water-cooled combustion chamber are quenched and saturated with water in a hydrator. An absorber bed of carbon or graphite rings may be mounted above the hydrator in the same structure to obtain more complete absorption of P2O5 and to assure that the gas stream is cooled to about 100oC. Weak acid from mist collection is sprayed on the absorber bed, and product acid at 75-85 percent H3PO4 leaves the hydrator through a heat exchanger.16

The P2O5 initially is hydrated and absorbed in the hot gas stream by direct contact with relatively strong acid. This is often followed by successive stages of scrubbing with progressively more dilute acid and finally, with incoming make-up water.17

Since most furnace grade phosphoric acid is used to make food-grade acid, the arsenic it contains must be removed in a purification step. The phosphoric acid is reacted with a small amount of hydrogen sulfide to precipitate arsenic sulfide which is removed by filtration.


None identified.

12 Kirk-Othmer Encyclopedia of Chemical Technology, 1982, Op. Cit., pp. 426-442.

13 Ibid.

14 Ibid.

15 Ibid.

16 Ibid.

17 Ibid.

EXHIBIT 4

FURNACE-GRADE PHOSPHORIC ACID PROCESSES


Atomizing Air

Phosphorous

Combustion Air

Product Acid

Cooling Water

Hea

t Ex

chan

ger

Phosphorous Combustion Air

Exit Gas to Hydrator

Exit Gasto MistCollectors

(a) Wetted-Wall Combustion Chamber (b) Air-Cooled Combustion Chamber

Phosphorous

Combustion Air

Cooling Water Overflow

To

Cooling Water to Jackets

Atomizing

(c) Water-Cooled Combustion Chamber

Hydrator

Phosphorous

To Mist Collector

Weak Acid from Mist Collector

Product Acid

Heat

(d) Hydrator/Absorber

Combustion Gas

Cooling Water

Exchanger

Air


The furnace process uses a refined mineral commodity and as such, is completely outside the scope of the Mining Waste Exclusion.

SECTION 3: Ancillary Processes

Feed and fertilizer plants, as well as sulfuric acid plants, often are co-located with phosphoric acid facilities. This section describes production of many products related to phosphoric acid. Exhibit 5 presents an overview of phosphoric acid and related product manufacturing operations. All of these ancillary processes use a saleable commodity (merchant grade phosphoric acid) as the primary raw material and, therefore, are outside the scope of the Mining Waste Exclusion.

Fertilizer Operations

About 95 percent of commercial phosphoric acid is used to make ammoniated fertilizer and animal feed. Several facilities produce ammoniated fertilizers such as DAP (diammonium phosphate), MAP (monoammonium phosphate), and GTSP (granular triple superphosphate). MAP and DAP are generated by ammoniating phosphoric acid and GTSP manufacturing involves reacting phosphate rock and phosphoric acid.18

Animal Feed Production

Ammonia is reacted with defluorinated P2O5 to produce the defluorinated ammonium phosphates Monofos and Duofos. Limestone is reacted with defluorinated P2O5 to produce the defluorinated calcium phosphates Dynafos and Biofos. IMC in Mulberry, FL produces up to 2,500 tons per day of these products.19

Superphosphoric Acid Operations

Superphosphoric acid is produced from concentrated (54 percent) acid by heating it in a shell and tube heat exchanger, routing it to an evaporator to remove the remainder of the free water, and concentrating the acid to 70 percent. This product can be sold or further filtered. Metallic phosphates are filtered out and routed to the granulated fertilizer feed.20

Liquid fertilizer may be produced by first diluting the superphosphoric acid back to 54 percent then ammoniating the acid. Liquid fertilizer is a low volume specialized product produced only on a limited basis.21

Silicofluoride Recovery

In order to produce low-fluorine animal feed supplements, P2O5 must be defluorinated. IMC in Mulberry, Florida defluorinates 600 tons per day of 54 percent P2O5 in a batch tank using silica to remove fluoride. IMC uses

18 U.S. Environmental Protection Agency, Supplemental Information on Phosphoric Acid Production: Alternative Management of Process Wastewater at Phosphoric Acid Facilities, Office of Solid Waste, December 1990, pp. A1-5.

19 Ibid., pp. A2-6.

20 Ibid.

21 Ibid.

EX H IB IT 5

OVER V IEW O F PH OSPH O RIC ACID AND RELATED PRO DUCTS PRODUCTION

(Adapted from: Supplem ental Inform ation on Phosphoric Acid Production, 1990, pp. A2 - 11.)

Rock Wet Rock Grinding Attack

H2O H2O H2O

Sulfuric Acid

M anufacture

Air

Sulfur

Filter Gypsum Waste

to Pond

0 - 46 - 0 Granular Tri-Super Phosphate

Uranium Recovery

Uranium

P2O5

EvaporationClarification Defluori-nation

0 - 53 - 0 Merchant

Acid

10 - 50 - 0 Mono-

Ammonium Phosphate

10 - 46 - 0 Di -

Am m onium Phosphate

Ammonia Ammonia 75% BPL

Rock

Fertilizer

Ammonia

Monofos Duofos

Dynafos BiofosLimestone

M ultifosSoda Ash

75% BPL Rock

Animal Feeds

16,000 gallons per minute of cooling pond water to condense vapors, which contain SiF4 and P2O5, from two evaporators using barometric condensers. Upon condensing, the SiF4 is converted to H2SiF6. IMC sends 6,000 gallons per minute of the flow to the Multifos plant; the remainder is returned to the cooling pond.22 USAC in Ft. Meade, Florida recovers 25 percent fluosilicic acid (FSA) as a by-product from the phosphoric acid evaporators and from reaction vapors evolved from the reaction stage. Fluorine compounds are recovered from the vapor in fluosilicic absorption towers at a rate of 55 tons per day. Seventy-five percent of the fluoride present in the vapors is removed. USAC sells its recovered fluosilicic acid to a nearby ALCOA plant that manufactures aluminum fluoride.23 Gardinier in Riverview, Florida also recovers FSA and in 1992 supplied 70 percent of the domestic market for drinking water fluoridation.24 Agrico in Uncle Sam, Louisiana collects FSA and either sells it or processes it in an on-site plant to produce silicon tetrafluoride.25 Agrico in Donaldsonville, LA sells the recovered FSA.

Multifos Plant

IMC reacts non-defluorinated 54 percent P2O5, soda ash, and phosphate rock in a high temperature calcining kiln to produce 300 tons per day of tricalcium phosphate, also known as Multifos, another low fluorine animal feed supplement. Wastewaters from this process are returned to the cooling ponds at IMC.26

Sulfuric Acid Production

Phosphate rock is reacted with sulfuric acid to make phosphoric acid. At many plants, sulfuric acid is produced on-site by burning sulfur. This process is exothermic and the heat generated is often used to run the plant. At Texasgulf in Aurora, North Carolina, fresh water is used to make sulfuric acid after being purified in a lime softening and ion exchange operation. Texasgulf has five sulfuric acid manufacturing process lines using double absorption with vanadium pentoxide catalysts. This produces 3.4 million tons of 95 percent acid annually.27 IMC in Mulberry, Florida produces 13,000 tons per day of 98.5 percent sulfuric acid.28 U.S. Agri-Chemicals in Fort Meade, Florida (USAC) produces sulfuric acid in two double absorption contact sulfuric acid manufacturing plants. Each plant has a capacity of 2,000 tons per day of 98 percent sulfuric acid.29 Gardinier in Riverview, Florida also manufactures sulfuric acid for the wet process.30


None identified.

22 Ibid., pp. A2-6.

23 Ibid., pp. A3-4.

24 Ibid., pp. A4-3.

25 Ibid., pp. A5-4.

26 Ibid.

27 Ibid., pp. A1-3.

28 Ibid., pp. A2-3.

29 Ibid., pp. A3-2.

30 Ibid., pp. A4-2.


These processes use a saleable mineral commodity as the primary raw material and as such, are completely outside the scope of the Mining Waste Exclusion.



None are identified.


Wet Process

Process wastewater and phosphogypsum are the primary waste streams from the wet process. These wastes have been classified as RCRA special wastes, and are exempt from Subtitle C regulation.

The fertilizer industry typically manages its waste streams in the aggregate. Aggregation allows heat that has built up in the system to assist natural evaporation in water management. Aggregate management of waste streams also is essential to maintaining the water balance at phosphate rock processing facilities. Control of the water balance requires close consideration of a number of factors, including the amount of rainfall, the watershed area, and evaporation rates. Generally across the industry, more than 90 percent of the water used is recycled. Because production and cooling are primary uses, water is generally recycled through cooling ponds. The constant reuse and recycling of water results in buildup of acidity to the point that the recirculating water has significant acid values that make it valuable for reuse and causes it to exhibit the corrosivity characteristic.31

Waste scale. This waste is generated at a rate of 41,700 to 208,300 metric tons per year and is generally sent to a cooling pond.32 This waste is not expected to be hazardous.

Furnace Process

The furnace process uses a refined mineral commodity (elemental phosphorus) and therefore is completely outside the scope of the Mining Waste Exclusion.

Arsenic sulfide sludge. Approximately 0.28 kg per kkg of product of arsenic sulfide is formed during product purification.33

Spent filter cake is a possible waste stream generated from the production of phosphoric acid by the furnace process.


32 U.S. Environmental Protection Agency, Technical Background Document, Data and Analyses in Support of the Regulatory Determination for Special Wastes from Phosphoric Acid Production, Office of Solid Waste, Special Waste Program, 1991.

33 U.S. Environmental Protection Agency, Supplemental Information on Phosphoric Acid Production: Alternative Management of Process Wastewater at Phosphoric Acid Facilities, Office of Solid Waste, December 1990, pp. A1-5.

3. Other Related Wastes

The other related wastes described below are commonly found at phosphoric acid facilities, but are outside of the scope of the Mining Waste Exclusion because they are associated with activities that are downstream of mineral processing and use a saleable commodity as the primary raw material.

Ammoniated Fertilizer Production

Process wastewater is a likely waste stream from ammoniated fertilizer production. In 1991, the waste generation rate for process wastewater from ammoniated fertilizer production was 132,517,000 metric tons per year.34 This wastewater may be discharged to a cooling pond and may have a low pH.

Sludge is a likely waste stream from ammoniated fertilizer production.

Animal Feed Production

Process wastewater is a likely waste stream from animal feed production.

Sludge is a likely waste stream from animal feed production. The 1991 waste generation rate for this waste stream was 400 metric tons per year.35

Superphosphoric Acid Production

Sludge is a likely waste stream from superphosphoric acid production.

Silicofluoride Recovery

Filter cake and process wastewater are the waste streams likely to result from silicofluoride recovery operations.

Sulfuric Acid Production

Process wastewater is a likely waste stream from sulfuric acid production. This waste is generated from an ancillary process and as such is outside the scope of this report. At Texasgulf in Aurora, North Carolina, this process wastewater from sulfuric acid production has a pH of about 10 and goes to a neutralization plant. In 1990, the wastewater was discharged via an NPDES outfall at a rate of 80-100,000 gpd.36 IMC in Mulberry, Florida and USAC in Ft. Meade, Florida create a cooling tower blowdown of pH 7 and a boiler blowdown of pH 11-12. USAC sends these wastewaters to a cooling pond. At IMC, sulfuric acid plant blowdown is kept separate from other process wastewater and is sent to a utility pond.37

34 Ibid.

35 U.S. Environmental Protection Agency, Newly Identified Mineral Processing Waste Characterization Data Set, Office of Solid Waste, Vol. I, August 1992, pp. I-2 - I-8.

36 U.S. Environmental Protection Agency, Op. Cit., 1990, pp. A1-3.

37 Ibid., pp. A2-3.

On-site production of sulfuric acid for acidulation of phosphate rock also generates secondary materials such as sulfuric acid production vessel cleanout residues. About once a year, small amounts of secondary materials, such as precipitates are removed from sulfuric acid process vessels and product storage tanks. 38

D. Non-uniquely Associated Wastes

Wastes associated with the ancillary processes often found at phosphoric acid plants are not uniquely associated because they are generated from chemical manufacturing activities, not from mineral processing. These wastes include the wastewaters, sludge, and filtercake (described above) resulting from the production of ammoniated fertilizer, animal feed, sulfuric and superphosphoric acid, and silicofluoride recovery.

Ancillary hazardous wastes may be generated at on-site laboratories, and may include used chemicals and liquid samples. Other hazardous wastes may include spent solvents (e.g., petroleum naptha), and acidic tank cleaning wastes. Non-hazardous wastes may include tires from trucks and large machinery, sanitary sewage, waste oil (which may or may not be hazardous) and other lubricants.



One commenter provided additional factual information about the phosphoric acid production process (COMM 45). This information, where appropriate, has been included in the sector report.

Sector-specific Issues

The commenter also addressed the potential negative implications of the Bevill mixture rule at phosphoric acid production facilities. The commenter noted that materials such as precipitates removed from sulfuric acid vessels and sulfuric acid spills may contain significant acid and sulfur values that can be useful in the phosphoric acid production process. The same may be true for wastes generated by recharging spent ion exchange resins (H2SO4 and NaOH). According to the commenter, the Bevill Mixture Rule requires these materials to be neutralized before being reused, resulting in a loss of the sulfur and acid values (COMM 45).


BIBLIOGRAPHY

Bartels, James J., and Theodore M. Gurr. "Phosphate Rock." From Industrial Minerals and Rocks. 6th ed. Society for Mining, Metallurgy, and Exploration. 1994. pp. 751-763.

Morse, David E. "Phosphate Rock." From Minerals Yearbook Volume 1. Metals and Minerals. U.S. Bureau of Mines. 1992. pp. 977-980.

"Phosphoric Acids and Phosphates." Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed. Vol. XVII. 1982. pp. 426-442.

U.S. Environmental Protection Agency. Supplemental Information on Phosphoric Acid Production: Alternative Management of Process Wastewater at Phosphoric Acid Facilities. Office of Solid Waste. December 1990. Appendix A.

U.S. Environmental Protection Agency. Newly Identified Mineral Processing Waste Characterization Data Set. Vol. I. Office of Solid Waste. August 1992. pp. I-2 - I-8.

U.S. Environmental Protection Agency. Newly Identified Mineral Processing Waste Characterization Data Set. Vol. III. Office of Solid Waste. August 1992. pp. 29-1 - 29-18.

U.S. Environmental Protection Agency. Technical Background Document, Data and Analyses in Support of the Regulatory Determination for Special Wastes from Phosphoric Acid Production. Office of Solid Waste, Special Waste Program. 1991.

U.S. Environmental Protection Agency. "Phosphoric Acid Production." From Report to Congress on Special Wastes from Mineral Processing. Vol. II. Office of Solid Waste. July 1990, pp. 12-1 - 12-61.

U.S. Environmental Protection Agency. "Phosphate Rock." 1988 Final Draft Summary Report of Mineral Industry Processing Wastes. 1988. pp. 2-120 - 2-127.

U.S. Environmental Protection Agency. Multi-Media Assessment of the Inorganic Chemicals Industry. Vol. 2. 1980. Chapter 8.

PLATINUM GROUP METALS (PGM)


The platinum-group metals refer to six metals: platinum, palladium, rhodium, ruthenium, iridium, and osmium. Commercially, the two most important metals are platinum and palladium. All of the platinum-group metals are valued for their corrosion resistance and their catalytic activity.1 According to the U.S. Bureau of Mines, ore containing the platinum-group metals is mined, concentrated, and smelted in Montana. The resulting platinum-group matte is sent to Belgium to be refined and separated. Additionally, platinum-group metals are recovered as byproducts of copper refining by two companies in Texas and Utah. Approximately 30 firms refine secondary metal domestically. Platinum-group metals are used by the following industries: automotive, electrical and electronic, chemical, dental, and medical. The metals are primarily used as catalysts in the automotive and petroleum refining industries.2 Domestic production was reported as 60,000 kilograms in 1994 (sales as reported to industry) and apparent domestic consumption was estimated at 127,000 kilograms during the same period.3 Exhibit 1 presents the names and locations of all the facilities involved in the production and refining of platinum-group metals.

The six platinum-group metals can be separated into three pairs: platinum and palladium, ruthenium and osmium, and rhodium and iridium. Each pair exhibits similar physical and metallurgical properties. Platinum and palladium are corrosion resistant and the most malleable. Ruthenium and osmium have the strongest abrasion resistance. Osmium alloys are used as pen tips and ruthenium is used as an electrical contact and as a titanium coating alloy. Rhodium and iridium are the least abrasion resistant and often used as alloying elements for platinum. Rhodium, palladium, and platinum are also used as an automotive catalyst for NOx reduction4, and platinum is used in both automobile oxygen sensors and spark plugs.5

EXHIBIT 1

SUMMARY OF PLATINUM-GROUP METALS PROCESSING FACILITIES

Facility Name Location Type of Operations (source)

Stillwater Mine Nye, MT Mining and Beneficiationa

Allied Signal Tulsa, OK Secondary (spent automotive catalysts)

Allied Precious Metals Tucson, AZ Secondary (solutions and sludges)

ASARCO Amarillo, TX Secondary

AT & T Metals Staten Island, NY Secondary (electronic scrap)

Colonial Metals MD Secondary (spent industrial catalysts)

Degussa Corp. South Plainfield, NJ Secondary (solutions, electronic scrap, catalysts)

1 J. Roger Loebenstein, "Platinum-Group Metals," from Minerals Yearbook Volume 1. Metals and Minerals, U.S. Bureau of Mines, 1992, p. 995.

2 J. Roger Loebenstein, "Platinum-Group Metals," from Mineral Commodity Summaries, 1995, pp. 126-127.

3 J. Roger Loebenstein, 1995, Op. Cit., p. 126.

4 U.S. Environmental Protection Agency, "Platinum-Groups Metals," from 1988 Final Draft Summary Report of Mineral Industry Processing Wastes, Office of Solid Waste, p. 3-159.

5 J. Roger Loebenstein, 1992, Op. Cit., p. 997.

EXHIBIT 1

SUMMARY OF PLATINUM-GROUP METALS PROCESSING FACILITIES (CONTINUED)


Eastern Smelting and Refining Corp.

Lynn, MA Secondary (solutions, sludges, catalysts)

Engelhard Corp Iselin, NJ Secondary (spent industrial catalysts, electronic scrap)

Gemini Industries Santa Ana, CA Secondary (spent industrial catalysts, petroleum catalysts)

Handy and Harman Fairfield, CT Secondary

Handy and Harman South Windsor, CT Secondary (filter cake, metallic scrap, spent automotive catalysts)

Hauser & Miller St. Louis, MO Secondary

JM Ney Co Bloomfield, CT Secondary

Johnson Matthey West Deptford, NJ Secondary (filter cake, spent automotive catalysts, solutions, unrefined ingot)

Kinsbursky Brothers Anaheim, CA Secondary (solutions, electronic scrap, spent automotive catalysts)

Kennecott Copper Magma, UT Hydrometallurgical precious metals plant recovers platinum from tankhouse slimes from ore.6

Leach and Garner Attleboro, MA Secondary

Leytess Metal and Chemical

New York, NY Secondary

LG Balfour CO Attleboro, MA Secondary

Martin Metals Los Angeles, CA Secondary (electronic scrap, solid scrap)

McRilley Mark Co. CA Secondary

Multimetco, Inc. Anniston, AL Secondary (spent automotive catalysts)

Noranda/Micrometallics Corp.

San Jose, CA Secondary (electronic scrap, filter cakes, sludges, solutions, catalysts, filter media)

Noranda Sampling Providence, RI Secondary (electronic scrap, solid scrap)

PGP Industries, Inc. Santa Fe, CA Secondary (spent industrial catalysts, sludges, electronic scrap)

Sabin Metals Rochester , NY Secondary (electronic scrap, filter cakes, solid scrap)

6 Kennecott Corporation. Comment submitted in response to the Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes. January 25, 1996. .

EXHIBIT 1

SUMMARY OF PLATINUM-GROUP METALS PROCESSING FACILITIES (CONTINUED)


Sipi Metals Chicago, IL Secondary (electronic scrap)

Southwest Smelter & Refining

Dallas, TX Secondary

Stern Metals Attleboro, MA Secondary

Techamet, Inc. Houston, TX Secondary (spent automotive catalysts, petroleum catalysts)

Technic, Inc. Providence, RI Secondary

Texas Instruments MA Secondary

Trifari, Krussman Providence, RI Secondary

William Gold Refining Buffalo, NY Secondary aStillwater Mines sends ore to its smelter facility in Columbus, MT.7

After the ores have been smelted, Stillwater Mines ships the platinum-group metal concentrate to Brussels, Belgium for refining. The concentrates are toll refined and although Stillwater Mines retains ownership of the metals, the products are generally sold overseas.8



Platinum-group metals can be recovered from a variety of different sources, including electrolytic slimes from copper refineries or metallic ores. Secondary platinum-group metals can also be recovered from used equipment, precious metal scrap, petroleum, and spent catalysts (both industrial and automotive). Each source is associated with a distinct recovery process. In one process the insoluble slimes from copper refining are collected and processed to recover any residual metal content. Alternatively, the production of platinum-group metals from ore involves mining, concentrating, smelting, and refining. In the concentrating step, platinum ore is crushed and treated by froth flotation. The concentrates are dried, roasted (sometimes), and fused in a smelter furnace. This step results in the production of a platinum-containing sulfide matte. Solvent extraction is used to separate and purify the six platinum-group metals in the sulfide matte.9 Secondary platinum group metals recovered from scrap and spent catalysts are refined and used in the fiber glass industry and various catalytic applications.

7 Personal Communication between ICF Incorporated and J. Roger Loebenstein, U.S. Bureau of Mines. October 17, 1994.

8 Ibid.

9 J. Roger Loebenstein, 1992, Op. Cit., pp. 995-996.


There are several methods for recovering and refining platinum-group metals, depending on the source material used. Exhibit 2 presents the process flow diagrams for the recovery process of the platinum-group metals from electrolytic slimes. Platinum metals can also be recovered from the ores or from scrap materials. After recovery and initial processing, the concentrates are sent for refining. Exhibit 3 presents a typical refining process used to separate each of the six platinum-group metals from a concentrate.

Recovery From Electrolytic Slimes

Often, platinum-group metals are recovered from the slimes that collect in the electrolytic refining cells used at copper refineries. These slimes are the insoluble material from impure copper anodes that are dissolved as part of the copper refining process. As shown in Exhibit 2, after the slimes are heated, H2S04 is added to the dried slimes which then undergo an acid digestion step. Following acid digestion, the slimes are often, but not always, roasted and then processed by several leaching steps to remove any remaining copper. After the leaching, the resultant decopperized slimes are melted with a soda-silica flux in a reverberatory furnace. This flux helps in the formation of a siliceous slag which is removed from the furnace. Air is then blown through the molten metal followed by the addition of a lime flux. The air oxidizes any remaining lead and the lead oxide forms a slag with the lime which is then removed from the furnace. The siliceous and lead slags are either recycled or sent to a lead smelter. Following slag removal, fused soda ash is added to the furnace to form soda slag which is also removed and sent off-site for tellurium and selenium recovery. The resultant metal is a dore alloy composed of gold, silver, and platinum-group metal and is processed to recover these metal values.10

Recovery From Metal Ores

Although alluvial deposits are the result of natural concentration processes involving weathering and gravity separation phenomena, further treatment is required to yield a product suitable for marketing and refining. At Stillwater, Montana, platinum and palladium are recovered via froth flotation of sulfide minerals. The ore is sent to a concentrator, followed by froth flotation, and then sent to a smelter operation in Columbus, Montana. The resulting precious metals matte (solid form) is then sent to MHO metallurgy in Belgium for refining.11

An alternative method of recovering platinum-group metals from ore in South Africa involves initial treatment to reduce the ore to a suitable size via crushing, followed by froth flotation to separate out the platinum-group metal particles. The flotation concentrates are separated into platinum-bearing minerals and free-metallic particles by conventional gravity methods. The remainder is further concentrated by smelting, oxygen blowing, magnetic separation, and pressure leaching.

The froth can be prepared for smelting by thickening, filtering, drying, and pelletizing. The pellets are smelted in an electric smelter with submerged-arc consumable electrodes. Fluxes and additions are made during smelting to obtain a matte that contains principally copper-nickel-iron and platinum-group metals. The matte is then treated by oxygen blowing to produce a high grade matte. The matte is crushed, ground, and magnetically separated. Any non-magnetic portion is treated by pressure leaching to release copper, nickel, and cobalt. The remaining solution is recirculated back into the magnetic stream and this mixture is then pressure leached, yielding a final concentrate. This concentrate along with the mineral material released previously are sent to a refinery for further treatment.12


11 Personal Communication between Jocelyn Spielman, ICF Incorporated and J. Roger Loebenstein U.S. Bureau of Mines, October 17, 1994.

12 "Platinum-Group Metals," Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed. Vol. XVIII, 1982, p. 234.

EXHIBIT 2 PLATINUM GROUP METAL RECOVERY FROM COPPER REFINING SLIMES

(Adapted from: 1988 Final Draft Summary Report of Mineral Industry Processing Wastes, 1988, pp. 3-158 - 3-163.)

Raw Slimes

Herreshoff Furnace

Dried SlimeH2SO4

Acid Digesters

Chain Roaster

Leach Tanks

Holding Tanks

Cementation Tanks

Scrubber and Cottrell

Caustic Leach Tanks

Dore Furnace

Neutralization Tanks

Slag Leaching Tank

Neutralization Tank

Scrubber and Cottrell

SO2

Waste Scrubber Mud

Solution Crude Se

To Selenium Plant

Fume

Leach Liquor

Scrap Copper

H2SO4

Leach Liquor to CuSO4 Plant or Liberator CellsCement Silver

Caustic Solution

Te-Pb Mud

Residue Anode Plant

Solution

Solution Neutralized Mud

Soda Slag

Caustic Slimes

Gas

NaOH H2O

Fluxes Gas

Solution

To Selenium Plant

To Anode Furnace

Slag

Gases

Dore Anodes

H2O

H2SO4

Parting Plant To Se Plant To Te Plant

Platinum Group Metals

Refining

Stillwater Mine sends the platinum-group metal concentrate out of the country for refining after it is processed at their smeltering facility in Columbus, Montana.13 Other platinum-group metals facilities in the United States refine secondary platinum-group metals from used equipment, scrap metals, petroleum, and spent catalysts. The refining process takes advantage of the solubility of platinum and palladium. Each platinum group metal is removed from the platinum-group metal concentrate in order of its solubility. Exhibit 3 presents the typical order of removal. In general, platinum and palladium are removed first, followed by rhodium, ruthenium, osmium, and iridium. Exhibit 3 also presents various compounds that may be produced through further purification of each individual platinum-group metal.

Platinum and palladium

Most refining procedures are based on the ready solubility of gold, platinum, and palladium in aqua regia and the ease with which gold can be reduced to the metallic form from the chloride solution by the addition of ferrous salts or sulfur dioxide. Solvent extraction is used as an alternative method for separating gold at some refineries.14 In the aqua regia refining process, platinum metal concentrates are treated with aqua regia to dissolve platinum, palladium, and gold. The other platinum-group metals (ruthenium, osmium, iridium, and osmium) and silver are insoluble. After the gold is separated from the solution either by reduction or solvent extraction, the remaining solution is treated with ammonium chloride to precipitate the platinum as ammonium chloroplatinate. The palladium remains in solution.15

The filtrate from the platinum-recovery contains palladium chloride and can be treated with ammonia and hydrochloric acid. The solution is heated to yield a solution of palladium (II) tetrammine dichloride. The addition of hydrochloric acid causes the formation of palladium dichloride diammine as a precipitate which can easily be dissolved in cold dilute ammonia. The resultant high-purity salt, when heated, can be converted readily into metal. Some refineries reduce pure palladium salt to palladium black with formic acid. The palladium black can then be ignited to form a palladium sponge. The aqueous byproducts of the formic acid are easier to handle than the corrosive fumes that result from firing the salts.16

The undissolved materials remaining after the aqua regia and any platinum-group metals recovered after the removal of platinum and palladium from solution are combined with concentrates high in rhodium, ruthenium, and iridium. Fluxing materials, such as lead carbonate plus carbon, are added, following which the mixture is heated. The molten charge is poured into a conical mold and solidified. After solidification, the slag is removed and the lead which contains rhodium, iridium, ruthenium, and silver is melted, granulated, and treated with nitric acid. The lead and silver are dissolved and removed, leaving an insoluble residue containing the platinum-group metals.17

13 Personal Communication between ICF Incorporated and J. Roger Loebenstein, U.S. Bureau of Mines, October 17, 1994.

14 "Platinum-Group Metals," 1982, Op. Cit., p. 238.

15 Ibid.

16 Ibid.

17 Ibid.

EXHIBIT 3

PLATINUM GROUP METAL REFINING


Platinum Metal Concentrates

Soluble HAuCl4, H2PtCl6, H2PdCl4

Precipitate, Impure Gold

Gold Anodes

Pure Gold, Sponge

Gold Grain

Precipitate, Impure Platinum Salt,

(NH4)2PtCl4

Filtrate H2PtCl6, H2PdCl4

Impure Platinum Sponge

Impure Sodium Platinum Chloride,

Na2PtCl6-

Pure Sodium Platinum Chloride

Na2PtCl6

Pure Platinum Salt, (NH4)2PtCl6

Platinum Sponge

Filtrate H2PdCl4

Precipitate, Impure Palladium Salt,

(Pd(NH3)2Cl2)

Precipitate, Pure Palladium Salt,

(Pd(NH3)2Cl2)

Palladium Black

Palladium Sponge

Flitrate, Traces of Platnum

Metal

Precipitate, Recovered

Platinum Metals

Filtrate

Waste Liquors

Aqua Regia

Solvent Extraction With Dibutyl Carbitol

Melting

Melting and Granulation

Ignition

Aqua Regia, Sodium Chloride

Bromate Hydrolysis

Ammonium Chloride

Ignition

Ammonium Chloride

Ammonia, Hydrochloric Acid

Formic Acid

Ignition

Ammonia, Hydrochloric Acid

Zinc Reduction

Waste Discharge

Electrolytic Refining

EXHIBIT 3 (Continued)

Insoluble Rh, Ru, Ir, Os, Ag

Lead Grain

Insoluble Rh, Ru, Ir, Os, Ag

Insoluble Ru, Ir, Os

Soluble Rhodim Sulfate

Rhodium Hydroxide, Rh(OH)3

Sodium Hydroxide

Sodium Bisulfate Fusion

Nitric Acid

Smelt with Litharge, etc.

Soluble Sodium Ruthenate,

Sodium Osmate

Sodium Peroxide Fusion

Insoluble Oxidized Iridium,

IrO2

Soluble Pb(NO3)2, AgNO3

Precipitate Lead Sulfate,

PbSO4

Filtrate AgNO3

Precipitate Silver Chloride

AgCl

Soda Ash, Charcoal, Smelt

Sulfuric Acid

Rhodium Chloride, H3RhCl6

Hydrochloric Acid Chlorine

Ruthenium Tetroxide,

Osmium Tetroxide

Aqua Regia, Ammonium Chloride

Impure Iridum Salt, (NH4)2IrCl6

Ammonium Rhodium Nitrate, (NH4)3Rh(NO2)6

Sodium Nitrate, Ammonium Chloride Purification and Reduction

Ruthenium Chloride,

Osmium Chloride

Purification and Reduction

Hydrochloric Acid

Iridium Powder

Ammonium Rhodium Chloride,

(NH4)3RhCl6

Hydrochloric Acid HNO3

Ruthenium Powder

Purification and Reduction

Silver Anodes

Silver Chrystals

Electrolytic Refining

Melting and Granulation

Silver Grain

Rhodium Sponge

Osmium Tetroxide

NaOH CH3OH

Sodium Osmate

KOH

Precipitate Potassium Osmate

Rhodium

The residue is then treated with sodium bisulfate and heated to 500o C to convert rhodium into the sulfate. After sodium hydroxide is added, the resultant crude hydroxide is precipitated out, washed, dissolved in hydrochloric acid (HCl), neutralized with sodium carbonate and treated with sodium nitrite. These steps yield the stable complex (NH4)3[Rh(NO2)6]. The contaminating base metals can be precipitated out of solution through hydrolysis, while leaving rhodium in solution. Rhodium can be precipitated by the addition of ammonium chloride, following which the ammonium salt is treated with HCl and the solution is passed through an ion exchange column. Ion exchange separates ammonium and any base metals from the high-purity rhodium, leaving it in solution. The rhodium is precipitated as finely divided metal by boiling with formic acid. After washing, the metal is ignited then cooled under hydrogen.18

Ruthenium

The ruthenium, osmium, and iridium residue from the bisulfate fusion is mixed with sodium peroxide and heated to 500o C, yielding sodium ruthenate and sodium osmate. These compounds are dissolved in water and treated with chlorine in a distillation apparatus. The resultant ruthenium tetroxide and osmium tetroxide are absorbed in dilute HCl. After boiling, the chloride solution is mixed with nitric acid to remove osmium. The mixture is then treated with ammonium chloride to yield ammonium chlororuthenate crystals. The latter are washed and ignited to yield ruthenium which is treated and cooled in hydrogen to give pure ruthenium powder.19

Osmium

Osmium tetroxide is produced in the same process as ruthenium tetroxide. After the osmium is removed from the ruthenium solution, the osmium tetroxide is then converted to sodium osmate. The addition of KOH causes the formation of precipitate potassium osmate. The salt is stored and can be converted to osmium metal.

Iridium

The insoluble iridium dioxide is converted with aqua regia to the chloride which is then precipitated with additional nitric acid and ammonium chloride. This salt is dissolved in a dilute ammonium sulfide solution in which impurities precipitate as sulfides, whereas the iridium remains in solution. Treatment with nitric acid and ammonium chloride yields pure ammonium chloroiridate which, upon ignition and reduction by hydrogen, yields pure iridium powder.


None Identified.

4. Beneficiation/Processing Boundary


18 Ibid.

19 Ibid.



EPA determined that for this specific mineral commodity sector, the beneficiation/processing line occurs between froth flotation and smelting for the recovery of platinum group metals from metal ores. EPA identified this point in the process sequence as where beneficiation ends and mineral processing begins because it is here where a significant chemical change to the sulfide mineral ore occurs. EPA also determined that all wastes generated during the recovery of platinum group metals from copper electrolytic slimes are mineral processing wastes. Therefore, because EPA has determined that all operations following the initial "processing" step in the production sequence are also considered processing operations, irrespective of whether they involve only techniques otherwise defined as beneficiation, all solid wastes arising from any such operation(s) after the initial mineral processing operation are considered mineral processing wastes, rather than beneficiation wastes. EPA presents the mineral processing waste streams generated after the beneficiation/processing line in section C.2, along with associated information on waste generation rates, characteristics, and management practices for each of these waste streams.



Although Exhibits 2 and 3 identify the following wastes as associated with the production of platinum-group metals, no characterization, generation, or management data are available for these wastes.

Concentration

Tailings and Filtrate. Tailings are generated during the froth filtration and sent to a tailings pond for disposal.

Wastewater. Wastewater from the thickening process is likely to contain heavy metals.


Recovery

Scrubber Off-gases. As shown in Exhibit 2, off gases are generated from the scrubber following roasting.

SO2 Waste. As shown in Exhibit 2, waste sulfur dioxide is produced from acid digestion.

Smelting

Slag. The slag generated during smelting is likely to contain metallic particles and may be crushed and blended with concentrate for recycling to the electric furnace.20 Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 5 metric tons/yr, 46 metric tons/yr, and 460 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may be recycled and may exhibit the characteristic of toxicity (lead and selenium). This waste is classified as a by-product.

Refining

Spent Solvents. After dissolving the material to be refined in aqua regia, a series of elements (e.g., gold, platinum, and palladium) are precipitated from the solution. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 300 metric tons/yr, 1,700 metric tons/yr, and 3,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristics of toxicity (lead and silver) and ignitability.

Spent Acids. Following solvent extraction, the insoluble platinum-group metals (e.g., rhodium, iridium, osmium, and ruthenium) are separated to yield pure metals. The resultant wastes from these processes would most likely be spent acids which might contain residual metals.21 Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 300 metric tons/yr, 1,700 metric tons/yr, and 3,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristics of toxicity (lead and silver), corrosivity, and reactivity.


Non-uniquely associated hazardous wastes may be generated at on-site laboratories, and may include used chemicals and liquid samples. Other hazardous wastes may include spent solvents (e.g., petroleum naphtha), and acidic tank cleaning wastes.



One comment was received to correct information about one facility in Utah. EPA has incorporated this new information into the document. (COMM 40)


None.

20 Gregg J. Hodges, et. al., "Stillwater Mining Co.'s precious metals smelter: From pilot to production, Mining Engineering, July 1991.


BIBLIOGRAPHY

Hodges, G., G. Roset, J. Matousek, and P. Marcantoni, "Stillwater Mining Co.'s precious metals smelter: From pilot to production," Mining Engineering, July 1991.

Loebenstein, J. Roger. "Platinum-Group Metals." From Mineral Commodities Summary. U.S. Bureau of Mines. 1995. pp. 126-127.

Loebenstein, J. Roger. "Platinum-Group Metals." From Minerals Yearbook Volume 1. Metals and Minerals. 1992. pp. 995-996 .

Loebenstein, J. Roger. "Platinum-Group Metals." From Mineral Facts and Problems. U.S. Bureau of Mines. 1985. pp. 595-608.

Personal Communication between Jocelyn Spielman, ICF Incorporated and J. Roger Loebenstein, U.S. Bureau of Mines. October 17, 1994.

"Platinum-Group Metals." Kirk-Othmer Encyclopedia of Chemical Technology. 3rd ed. Vol. XVIII. 1982. pp. 228-239.

Public Comment submitted in response to the Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes, January 25, 1996.

U.S. Environmental Protection Agency. "Platinum-Group Metals." From 1988 Final Draft Summary Report of Mineral Industry Processing Wastes. Office of Solid Waste. 1988. pp. 3-158 - 3-163.

PYROBITUMENS, MINERAL WAXES, AND NATURAL ASPHALTS


Bituminous materials comprise a group of hydrocarbons including pyrobitumens, mineral waxes, and asphalts. Pyrobitumens are mined predominately in Utah and are used in rubber, paints, varnishes, and insulating and waterproofing compounds.

Mineral waxes are not present in the United States as a natural substance, and therefore, must be extracted from lignite or cannel coal. Although coal exists in many parts of the United States, the only known production of mineral waxes from coal occurs in California. The use of this extraction product, known as "Montan Wax," is limited to paints, wood fillers, floor polish, rubber mixtures, and candles.

In the United States, naturally occurring asphalt (gilsonite) is found in commercial quantities only in eastern Utah and western Colorado. There are three types of naturally occurring asphalt: native asphalt (bitumen), lake asphalt, and rock asphalt.1 Asphalts have a variety of uses including paving, flooring, roofing, and waterproofing. American Gilsonite in Bonanza, Utah is the world's largest producer and exporter of gilsonite (natural asphalt). The only other producer of natural asphalt is Ziegler Chemical and Mineral Corporation, also in Utah.



The production processes associated with the production of pyrobitumens, mineral waxes, and natural asphalts are limited to a few simple operations, including extraction, grinding, blending, and packaging. Exhibits 1 through 3 present simplified process flow diagrams for the production of pyrobitumens, mineral waxes, and natural asphalts. The production processes and wastes associated with each mineral commodity are discussed below.


Pyrobitumens

As shown in Exhibit 1, the production process for pyrobitumens consists of cracking in a still, recondensing, and grading. Due to the low cost and availability of petroleum refining substitutes, the production of pyrobitumens appears to be low.

Mineral Waxes

As shown in Exhibit 2, mineral wax processing consists of solvent extraction from lignite or cannel coal. Cannel coals yield a material that contains 60 to 90 percent light yellow or brown waxy substances. The crude wax is refined by extracting, typically with a mixture of benzene and methanols. Distilling the solvent leaves a wax too darkly colored to be used without added refining. Acid mixtures are used to oxidize and remove the dark materials, leaving a series of bleached waxes.2 The extraction product is known as "Montan Wax." Extraction solvents used in the production of mineral waxes may be listed in 40 CFR 261 Subpart D.3

1 "Asphalt," Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. III, 1992, pp. 689-724.

2 "Lignite," Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. XV, 1995, p. 316.

3 U.S. Environmental Protection Agency, Technical Background Document, Development of the Cost, Economic, and Small Business Impacts Arising from the Reinterpretation of the Bevill Exclusion for Mineral Processing Wastes, Office of Solid Waste, 1989, pp. A-9.

EXHIBIT 1

PYROBITUMEN PROCESSING

(Adapted from: 1988 Final Draft Summary Report of Mineral Industry Processing Wastes, 1988.)

Pyrobitumens

Cracking Still

(1) Waste Catalyst (2) Still Bottoms

Condensation

Grading Pyrobitumen Products

Source: 1988 Final Draft Summary Report of Mineral Industry Processing Wastes. 1988.

EXHIBIT 2

MINERAL WAX PRODUCTION


Lignite or Cannel Coal

Montan Wax (1) Spent Solvent (2) Spent Coal

Solvent Extraction

Source: 1988 Final Draft Summary Report of Mineral Industry Processing Wastes, 1988.

Natural Asphalts

American Gilsonite operates a 110 ktpy facility in Bonanza, Utah. Mine development begins with the boring of shafts. The shafts are equipped with steel inserts that are comprised of four pipes equally spaced around the perimeter of the shaft. Once a shaft is bored, inserts are lowered into the borehole. As each section is lowered into the shaft the next section is lined up with it, and the two are welded together at the surface. This procedure is repeated until the inserts line the shaft from top to bottom. When a mine is worked out the liner assembly is pulled and reused. Hand-held pneumatic chipping hammers with moilpoint bits are used to break out the ore. Broken ore flows by gravity to the toe of the sloping face at the floor of the drift. From there it is airlifted to the surface through a pipe. When air lifted ore reaches the surface it enters a baghouse. The larger pieces drop first, and the rest is collected in filter bags. All solids are discharged into elevated storage bins and are then transferred by truck to a processing plant.

American Gilsonite's plant consists of concrete storage silos, truck receiving bins, a vibrating bed dryer, pulverizing machinery, and packaging equipment. Pneumatic conveying systems and sophisticated dust control equipment are state-of-the-art and allow for the handling of gilsonite in large quantities. Before entering the processing plant, gilsonite ore is segregated by grade in receiving bins. From these bins the ore is processed through a vibrating bed dryer, where excess moisture is removed. It is then passed over a double-deck screen, where it is classified according to particle size for storage in silos. From the silos, ore is fed to product bins from which it is either loaded directly as bulk product, fed to a bagging machine, or fed to a pulverizer. Pulverized product is segregated into product bins from which it can be loaded directly as bulk product or packaged at a second bagging machine.4 Exhibit 3 contains the natural asphalt production process diagram.


None identified.




EPA approached the problem of determining which operations are beneficiation and which (if any) are processing in a step-wise fashion, beginning with relatively straightforward questions and proceeding into more detailed examination of unit operations, as necessary. To locate the beneficiation/processing "line" at a given facility within this mineral commodity sector, EPA reviewed the detailed process flow diagram(s), as well as

4 Harry D. Lewis, "Gilsonite," from Industrial Minerals and Rocks, Society of Mining, Metallurgy, and Exploration, 1994, pp. 535-541.

EXHIBIT 3

NATURAL ASPHALT PRODUCTION


Rock Asphalt

Size Reduction

Grading

Asphalt Products Blending

Source: 1988 Final Draft Summary Report of Mineral Industry Processing Wastes, 1988.

information on ore type(s), the functional importance of each step in the production sequence, and waste generation points and quantities presented above.

Pyrobitumens

EPA determined that for pyrobitumens, the beneficiation/processing line occurs when the pyrobitumens are thermally cracked in a still to produce a significantly altered material. Therefore, because EPA has determined that all operations following the initial "processing" step in the production sequence are also considered processing operations, irrespective of whether they involve only techniques otherwise defined as beneficiation, all solid wastes arising from any such operation(s) after the initial mineral processing operation are considered mineral processing wastes, rather than beneficiation wastes. EPA presents below the mineral processing waste streams generated after the beneficiation/processing line, along with associated information on waste generation rates, characteristics, and management practices for each of these waste streams.

Mineral Waxes and Natural Asphalts

Based on a review of the processes, there are no mineral processing operations involved in the production of mineral waxes or natural asphalts.



Pyrobitumens

None identified.

Mineral Waxes

Probable wastes from the production of mineral waxes include spent solvents and spent coal.

Natural Asphalt

None identified.


Pyrobitumens

Still bottoms. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 2 metric tons/yr, 45,000 metric tons/yr, and 90,000 metric tons/yr, respectively. We used best engineering judgement to determine that this waste may exhibit the characteristic ignitability.

Waste catalyst. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 2 metric tons/yr, 10,000 metric tons/yr, and 20,000 metric tons/yr, respectively. We used best engineering judgement to determine that this waste may exhibit the characteristic of toxicity for cadmium and selenium. This waste may be recycled and is classified as a spent material.

Mineral Waxes

None identified.

Natural Asphalt

None identified.


Non-uniquely associated and ancillary hazardous wastes may be generated at on-site laboratories, and may include used chemicals and liquid samples. Other hazardous wastes may include spent solvents, and acidic tank cleaning wastes. Non-hazardous wastes may include tires from trucks and large machinery, sanitary sewage, and waste oil other lubricants.


EPA received no comments that address this specific sector.

BIBLIOGRAPHY

"Asphalt." Kirk-Othmer Encyclopedia of Chemical Technology. 4th ed. Vol. III. 1992. pp. 689-724.

Lewis, Harry. "Gilsonite." From Industrial Minerals and Rocks. 6th ed. Society for Mining, Metallurgy, and Exploration. 1994. pp. 535-541.

"Lignite." Kirk-Othmer Encyclopedia of Chemical Technology. 4th ed. Vol. XV. 1995. p. 316.

U.S. Environmental Protection Agency. Technical Background Document, Development of the Cost, Economic, and Small Business Impacts Arising from the Reinterpretation of the Bevill Exclusion for Mineral Processing Wastes. Office of Solid Waste. 1989. pp. A-9.

U.S. Environmental Protection Agency. "Bituminous Materials." From 1988 Final Draft Summary Report of Mineral Industry Processing Wastes. 1988. pp. 2-70 - 2-76.

RARE EARTHS


The rare earth elements are comprised of scandium, yttrium, and 15 lanthanide elements, of which cerium, lanthanum, and neodymium are the most abundant. While rare earth elements are found in several minerals, almost all production comes from less than 10 minerals, primarily monazite and bastnasite. Because the scandium industry is, for the most part, separate and distinct from the yttrium and lanthanide industries it is the subject of a separate commodity summary (see the chapter on scandium).

The United States is a major producer and consumer of rare earth ores and compounds that are used in petroleum fluid cracking catalysts, chemical and pollution-control catalysts, metallurgical applications, glass and ceramics, permanent magnets, phosphors, and electronics.1

In 1993 two domestic mines, Molycorp, Incorporated and RGC (USA) Minerals Incorporated, produced rare earths. Molycorp, Inc.’s facility in Mountain Pass, CA is the sole producer of rare earth minerals from bastnasite ore.2 In 1995, Molycorp supplied over 60 percent of U.S.-produced cerium products, with competition from China, the former states of the U.S.S.R., and India.3 The use of bastnasite ore is preferred in the market over monzanite ore because of due to lower concentrations of natural radionuclides which results in lowers worker exposures to low level radiation.4 The Mountain Pass facility is an integrated mining and beneficiation/processing facility.5 Twenty facilities produce rare earth materials. Exhibit 1 presents the names, locations, and products of the facilities involved in the production of rare earth materials, however, not all of these facilities engage in primary mineral processing activities.



Most production of rare earth elements is from the minerals monazite and bastnasite. Processing of these ores is by sulfuric and hydrochloric acid digestion. The compounds recovered from these processes must be processed further to produce and recover rare earth metal compounds. Processes include solvent extraction and reduction.6 Exhibits 2 through 6 present typical process flow diagrams for the production of rare earths.

Bastnasite is produced only by Molycorp at Mountain Pass, California. It is produced as a mineral concentrate and consumed captively at this facility. Monazite is produced by Associated Minerals at Green Cove Springs, Florida as a byproduct of beach sand mining for titanium and zircon minerals.7

1 James Hedrick, "Rare Earths," from Mineral Commodity Summaries, U.S. Bureau of Mines, January 1995, pp. 134-135.

2 Molycorp, Inc., Comment submitted in response to the Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes, January 25, 1996.

3 Ibid.

4 Ibid.

5 Ibid.

6 Ibid.

7 U.S. Environmental Protection Agency, Technical Background Document, Development of the Cost, Economic and Small Business Impacts Arising from the Reinterpretation of the Bevill Exclusion for Mineral Processing Wastes, Office of Solid Waste, 1989, pp. A-21 - A-22.

2. Generalized Process Flow

Mining

At Mountain Pass, Molycorp mines rare earth ore in an open pit approximately 100 meters deep. Blast holes drilled at 3 to 4 meter spacing are routinely assayed for total rare earth oxides and other elements by fluorescence methods. Approximately 300 kilotons per year are mined with a stripping ratio of 5:1. The ore is crushed and blended in stockpiles that contain about 40 kilotons and fed to a mill located less than 100 meters from the pit.8

EXHIBIT 1

SUMMARY OF RARE EARTHS PROCESSING FACILITIES

Facility Name Location Products

Crucible Materials Elizabethtown, KY Rare earth magnets

Delco Remy Division of General Motors

Anderson, IN Rare earth magnets, neodymium-iron-boron magnet alloys

Hitachi Magnetics Edmore, MI Rare earth magnets

IG Technologies Valparaiso, IN Rare earth magnets

Molycorp9 Mountain Pass, CA Bastnasite mine

Mountain Pass Mine & Mill Mountain Pass, CA Uncertain

Neomet West Pittsburgh, PA Neodymium-iron-boron magnet alloys

Nord Resources Jackson, NJ Uncertain

Reactive Metals & Alloys Corp. West Pittsburgh, PA Mischmetal

Research AZ Uncertain

RGC (USA) Mineral Inc. Green Cove Springs, FL Byproduct monazite

Rhone-Poulenc Chemicals Co. Phoenix, AZ Mineville, NY Freeport, TX

Neodymium-iron-boron magnet alloys Uncertain Uncertain

W.R. Grace Chattanooga, TN Uncertain

Phoenix,

8 James Hedrick, "Rare Earths, the Lanthanides, Yttrium, and Scandium," from Minerals Yearbook Volume 1. Metals and Minerals, U.S. Bureau of Mines, 1992, pp. 1035-1047.

9 Molycorp, Inc., 1996, Op. Cit

Molycorp's mine was the leading producer of rare earths in both the United States and the rest of the world in 1992. In 1993, mine production decreased from the 1992 level of 22,713 tons to 16,465 tons of rare earth oxides.10

Almost all mining of heavy mineral sands from surface placer deposits is done by floating cutterhead or bucket wheel dredges that concentrate the heavy minerals onboard and discharge the unwanted tailings back into previously mined areas. An onboard wet mill separates the heavy minerals from the lighter weight fraction through wet gravity equipment that includes a series of screens, hydroclones, spirals, and cones. Wet mill mixed heavy mineral concentrate is sent to a dry mill to separate the individual heavy minerals and produce a concentrate. Dry mill processing includes a combination of scrubbing, drying, screening, electrostatic, electromagnetic, magnetic, and gravity processes. Gravity methods include the use of jigs, spiral and cone concentrators, and shaking tables. Sizing and preconcentration commonly is performed at the mine site by trommels, shaking screens, and gravity separation. Many dredges have such facilities on board or utilize floating preconcentration plants.11 Monazite can be separated from zircon by electrostatic methods such as electromagnetic or gravity methods. Xenotime is usually separated from monazite by precise gravity methods. Some deposits may require acid leach treatment and calcining to eliminate iron oxide or other grain coatings.

Some sand deposits, too difficult to mine by dredging, are mined using dry methods. Ore is stripped with scrapers, bulldozers, and loaders. Sands recovered by these techniques are crushed, screened, and processed by the wet mill equipment described above.

Recovery

Monazite Ore Processing

Rare earth metals are recovered as oxides from monazite ore by sulfuric acid digestion (Exhibit 2). The ore undergoes grinding, spiraling, or other similar operations for the initial coarse purification of the ore. Magnetic separation removes the magnetic ore constituents which can be processed separately or discarded as waste. The refined ore is then digested with sulfuric acid at 200-220oC. Rare earth sulfates and thorium sulfates are then dissolved and removed from the waste monazite solids by filtration. Rare earth elements are then precipitated as oxalates or sulfates. These precipitates undergo caustic digestion or roasting to form rare earth oxides which are finally recovered by filtration. The resulting filtrate is discarded as waste.12

Bastnasite Ore Processing

To recover rate earths from bastnasite ore, the ore is crushed, ground, classified, and concentrated to increase rare earth concentrations.13 These processes, as well as the subsequent beneficiation and mineral processing steps, are described in the following paragraphs. The final filtration step yields lead and iron filter cake while the final drying step yields the rare earth concentrates.14

10 U.S. Bureau of Mines, Rare Earths Annual Report, 1993.

11 Stephen B. Castor, "Rare Earth Minerals," from Industrial Minerals and Rocks, 6th ed., Society for Mining, Metallurgy, and Exploration, 1994, pp. 827-837.

12 U.S. Environmental Protection Agency, "Rare Earths," from 1988 Final Draft Summary Report of Mineral Industry Processing Wastes, 1988, pp. 3-164 - 3-174.

13 Molycorp, Inc., Comment submitted in response to the Second Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes, May 12, 1997.

14 Ibid.

EXHIBIT 2

RECOVERY OF RARE EARTHS FROM MONAZITE BY THE SULFURIC ACID PROCESS


Monazite Ore

Spirals Waste Tailings

Magnetic Magnetic FractionsSeparation

Grinding

DigestionH2SO4 200 - 220 o C

Slurry

Dissolution of Cold Water Rare Earths and

Thorium Sulfates

Filtration Solids Waste Monazite

Filtrate

Double Sulphate Precipitation NaOH and Water

Filtration Cake Caustic Digestion

Filtrate Slurrry

Recovery of Filtration Waste Thorium and Minor Filtrate Rare Earth Fractions

Rare Earth Hydroxide Cake

EXHIBIT 3RECOVERY OF RARE EARTH CHLORIDES FROM BASTNASITE ORE

(Adapted from: 1988 Final Draft Summary Report of Mineral Industry ProcessingWastes, 1988, pp. 3-164 - 3-174., and Molycorp, Inc., Comment on Second

Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to NewlyIdentified Mineral Processing Wastes, May 12th, 1997.)

Bastnasite Ore

Crushing, Screening, and Blending

Classification

Waste Tailings

Waste TailingsFlotation

Leaching (HCl)

60-65% Rare Earth Oxides

Roasting CO21200° F

Soluble Lanthanides

Fe and Pb Precipitation

Pb/Fe Filter Cake

Lanthanide Concentrates to Solvent Extraction

96% Cerium

Acid Leaching / Digestion (HCl)

Rare Earth Concentrates

Slurry

Cerium Thickening, Filtering, Drying,

Purification

Cerium Solids 85% Rare Earth Oxides

Purification/Concentration

Flotation

Flotation is used at Mountain Pass to make a bastnasite concentrate containing about 60-65 percent rare earth oxides.15 This concentrate is either used on-site as feed for chemical separation of rare earth elements, leached to produce a 70 percent rare earth oxide concentrate, or shipped off-site to customers.

Recovery of Concentrate

Recovery of rare earth concentrates from monazite and xenotime is accomplished by digestion in a hot concentrated base or acid solution. At Rhone-Poulenc Inc. plants, which process most of the world's monazite, rare earth elements are extracted in a concentrated solution of sodium hydroxide at 140 to 150oC. After cooling, hydroxides of rare earth elements and thorium are recovered by filtration, and thorium is separated by selective precipitation or dissolution. At Mountain Pass, bastnasite is roasted at 1200oF to drive off CO2 and leached/digested with dilute, chilled HCl to dissolve most of the trivalent rare earth elements.16, 17 Specifically, in this “leach” step the solid lanthanide ore is reacted with HCl to produce lanthanide chloride. This leaching also produces lead and iron chloride wastes, which are subsequently reacted with ammonia and sodium hydrogen sulfide, respectively, to form small volumes of solid iron hydroxide and lead sulfide wastes. In this step, cerium oxide is also leached to produce a higher concentrate cerium oxide product. In this roasting/leaching sequence, the roasting step converts cerium (III) fluorocarbonate to cerium (IV) oxide, which then undergoes leaching with HCl to produce a cerium oxide concentrate. This second leach step produces a final or intermediate product (low grade cerium concentrate) that does not undergo further beneficiation or processing.18 The residue, cerium concentrate, is sold as a polishing abrasive.19, 20

The rare earth hydroxide and chloride concentrates recovered from sulfuric acid and hydrochloric acid leaching/digestion operations must undergo further processing to produce and recover individual rare earth metal compounds such as fluorides, nitrates, carbonates, oxides, and pure metals, for a variety of applications. Processes include solvent extraction and reduction.

Rare Earth Separation by Solvent Extraction

To separate individual rare earths in a mixture from each other, an aqueous solution containing rare earth salts is sent countercurrent to an immiscible organic stream which selectively extracts one rare earth from the others. Several stages of extractions are needed to separate each rare earth metal. Each organic stream is then scrubbed with an aqueous stream to transfer the rare earth element into an aqueous phase. Because all of the products are aqueous solutions, the spent solvents leave the process as wastes.21 Exhibit 4 presents a process flow diagram for solvent extraction.

15 Ibid.

16 Molycorp, Inc., 1997, Op. Cit.


18 U.S. Environmental Protection Agency, Lowrance, Sylvia K. to Mark A. Smith, Attorney, Unocal Corporation, April 7, 1992.

19 Stephen Castor, 1994, Op. Cit., pp. 827-837.



EXHIBIT 4

RARE EARTH SEPARATION BY SOLVENT EXTRACTION


Rare Earth Nitrate Solution (La, Pr, Nd, Sm)

Extraction and

Scrubbing

Tri-butyl Phosphate Solution

Nitric Acid Scrub

Batch Extraction

Solvent (Sm, Nd, HNO3)

Concentrate or Precipitate and

Redissolve

Aqueous Solution (Pr, La)

Aqueous (Sm, Nd)

Water

Waste Solvent

Solvent

Scrub

Back Extract

Waste Solvent

Precipitate and

Redissolve

Extraction and

Scrubbing

Solvent (Sm)

Back Extraction

Aqueous Sm Aqueous Nd

Extraction and

Scrubbing

Solvent (Pr)

Back Extraction

Aqueous La Aqueous Pr

Solvent

Scrub

Back Extract

Waste Solvent

Calcium Reduction

High purity rare earth metals can be produced by the metallothermic reduction of rare earth halides. This process is used when 99.99 percent purity is required. After converting the rare earths into fluorides, they are reduced to the metallic state through contact with calcium or barium at high temperatures.22 Exhibit 5 presents a flow diagram for calcium reduction.

Ten of the rare earths (lanthanum, cerium, praseodymium, neodymium, gadolinium, terbium dysprosium, holmium, erbium, and lutetium as well as scandium, and yttrium) are produced by calcium reduction. The raw material form of these metals is the metal fluoride. The individual metal fluoride is placed with calcium metal into a reduction vessel where a heat-driven reaction produces pure rare earth metal and calcium fluoride. The metals are further purified by melting in a vacuum to remove impurities. Casting is dependent upon the form in which a buyer wants the metal. Non-contact cooling water is used to cool both the reduction vessels and the melting and casting equipment.

Mischmetal

Mischmetal Production

Wet rare earth chlorides or hydrated rare earth compounds must be stripped of their water before electrolytic reduction can take place in order to prevent decay of the graphite anode during electrolysis. The anode could be decayed by the reaction of the liberated oxygen in the electrolyte with the carbon anode to form carbon dioxide. Batch or continuous mode dryers may be used. Both gas heat and electric heat have been used to run the dehydration furnaces.23

Dry rare earth chlorides are reduced to mischmetal in electrolytic cells. Batch process electrolysis reduces the rare earth salts to metal in 8 to 12 hours. Excess slag is removed and may be sold for its rare earth chloride content. Following reduction, the mischmetal is cast into bars or ingots for future uses.24 Exhibits 6 and 7 present process flow diagrams for mischmetal production.

Mischmetal Reduction

Mischmetal is an alloy typically composed of cerium, lanthanum, neodymium, praseodymium, other rare earth metals, and iron. Mischmetal processing reduces the oxide form of the rare earth metals (samarium, europium, and ytterbium) to an elemental form. In this reaction, the mischmetal acts as a reducing agent and is oxidized to a mixture of rare earth metal oxides. The process is performed at a low pressure and a temperature below the melting point so that the metals vaporize or sublime. The pure metal is condensed and collected in a crystalline mass of high purity. These solids may be crushed into powder or melted and cast if a solid product form is desired.


None identified.

22 Ibid.

23 U.S. Environmental Protection Agency, Development Document for Effluent Limitations Guidelines and Standards for the Nonferrous Metals Manufacturing Point Source Category, Volume X, Office of Water Regulations and Standards, May 1989, pp. 5376-5384.

24 Ibid.

EXHIBIT 5

CALCIUM REDUCTION PROCESS


Rare Earth CalciumFluorides

Non-Contact Cooling

Calcium Reduction

Reduced Metal

Melting and

Casting

Pure Rare Earth Metal Ingot

Impurities

Non-Contact Cooling

Calcium Fluoride





EPA determined that for rare earths and mischmetal, the beneficiation/processing line occurs between ore preparation and acid digestion when the ore is vigorously attacked with concentrated acids, resulting in the physical destruction of the ore structure.

After careful analysis of Molycorp’s process information, EPA determined in 1991 and 1992, that two distinct operations occur during what Molycorp classifies as its “second leach step.” The Agency believes that those determinations are still appropriate. Molycorp submitted extensive comments on EPA’s conclusions, which are addressed in the response to comments document in the record .

Because EPA has determined that all operations following the initial "processing" step in the production sequence are also considered processing operations, irrespective of whether they involve only techniques otherwise defined as beneficiation, all solid wastes arising from any such operation(s) after the initial mineral processing operation are considered mineral processing wastes, rather than beneficiation wastes. EPA presents below the

mineral processing waste streams generated after the beneficiation/processing line, along with associated information on waste generation rates, characteristics, and management practices for each of these waste streams.


Rare earth element ores and commodities, as well as byproducts and waste materials from rare earth processing, are naturally radioactive, due to contained thorium.


Tailings and magnetic fractions are possible rare earths extraction/beneficiation wastes.


Off-gases from dehydration from the furnaces are treated by water or alkaline scrubbers to remove particulates and acid. The treated gases are vented.25 Existing data and engineering judgment indicate that this waste does not exhibit any characteristics of a hazardous waste. Therefore, the Agency did not evaluate this material further.

Spent iron hydroxide cake. Existing data and engineering judgment indicate that this waste does not exhibit any characteristics of a hazardous waste. Therefore, the Agency did not evaluate this material further.

Spent lead and sand filter cinders. This waste contains waste components (e.g., lead) that originate from the orebody as a result of direct contact with the mineral values (i.e., lanthanides) being processed.

Spent monazite solids. Existing data and engineering judgment indicate that this waste does not exhibit any characteristics of a hazardous waste. Therefore, the Agency did not evaluate this material further.

Spent offgases from electrolytic reduction. Off-gases from electrolytic reduction include chlorine gas, carbon monoxide and carbon dioxide gases from the carbon in the graphite anodes, and hydrochloric acid fumes. These gases are contacted with water to both cool the gases and to absorb particulates and hydrochloric acid vapors. The partially cleansed gases are then contacted with sodium hydroxide solution, resulting in the formation of sodium hypochlorite. This solution may be sold as a byproduct26, and it may not exhibit any characteristics of a hazardous waste. Therefore, the Agency did not evaluate this material further.

Waste filtrate. Existing data and engineering judgment indicate that this waste does not exhibit any characteristics of a hazardous waste. Therefore, the Agency did not evaluate this material further.

Waste solvent. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 2,000 metric tons/yr, 1,000,000 metric tons/yr, and 2,000,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristic of ignitability. EPA does not considers this material to be a waste, because it is fully recycled.

Spent lead filter cake. This waste may be stabilized with a polysilicate material and then reinserted into the process for extraction of additional cerium. Tailings containing carbonates are used to precipitate iron. The resulting lead filter cake may exhibit the characteristic of toxicity for lead. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 3,300 metric tons/yr, 4,200 metric tons/yr, and 5,000 metric tons/yr, respectively. EPA believes this material is fully recycled to recover metal values, and not land stored.

25 U.S. Environmental Protection Agency, 1989, Op. Cit, pp. 5376-5446.

26 Ibid.

Lead backwash sludge. Existing data and engineering judgment indicate that this waste does not exhibit characteristics of a hazardous waste. Therefore, the Agency did not evaluate the material further. Further, Molycorp, Inc. asserted that its Mountain Pass facility no longer produces this waste.

Waste zinc contaminated with mercury. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 200 metric tons/yr, 45,000 metric tons/yr, and 90,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristic of toxicity for mercury. One firm, Molycorp, Inc., asserted that its Mountain Pass facility no longer produces this waste.

Solvent extraction crud. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 200 metric tons/yr, 45,000 metric tons/yr, and 90,000 metric tons/yr, respectively. However, this waste is only generated at one facility and one firm, Molycorp, Inc., indicated that its Mountain Pass facility no longer produces this waste. We used best engineering judgment to determine that this waste may exhibit the characteristic ignitability. This waste may be recycled and formerly was classified as a spent material.

Spent surface impoundment liquids are a likely waste stream from rare earth production. Surface impoundment liquids were generated at a rate of 477,000 metric tons per year in 1991.27 Waste characterization data are presented in Attachment 1. This waste is not expected to be hazardous.

Spent surface impoundment solids. This waste stream was generated at a rate of 100 metric tons per year in 1991 and may be toxic for lead.28 This waste is not expected to be hazardous. Waste characterization data are presented in Attachment 1.

Lanthanide Production

Spent ammonium nitrate processing solution is a possible waste stream from lanthanide separation. The 1991 waste generation rate for the sector was 14,000 metric tons per year. This waste may exhibit the characteristic of corrosivity.29 Attachment 1 presents waste characterization data.

Cerium Production

Process wastewater. This waste stream may be toxic for lead as well as contain detectable levels of ammonium. This wastewater may also be corrosive. The 1991 waste generation rate for the sector was 7,000 metric tons per year.30 Waste characterization data are presented in Attachment 1. This waste may be recycled and formerly was classified as a spent material.

Mischmetal Production

Spent scrubber liquor from wet air pollution control is generated from mischmetal production. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 100 metric tons/yr, 500,000 metric tons/yr, and 1,000,000 metric tons/yr, respectively. We used best engineering

27 U.S. Environmental Protection Agency, 1992, Op. Cit., Vol. I, pp. I-2 - I-8.

28 Ibid.

29 Ibid.

30 Ibid.

EXHIBIT 6

MISCHMETAL REDUCTION PROCESS


Rare Earth Misch Metal Oxide Metal

Non-Contact Cooling

Mischmetal Reduction (Vacuum

Distillation)

Mixed Rare Earth Oxides

Crystalline Rare Earth

Metal Crushing

and Packaging

Rare Earth Metal Product

judgment to determine that this waste may exhibit the characteristic of corrosivity. This water may be recycled or discharged to wastewater treatment. This waste formerly was classified as a spent material.

EXHIBIT 7

MISCHMETAL PRODUCTION PROCESS

(Adapted from: Development Document for Effluent Limitations Guidelines, 1989, pp. 5376 - 5446.)

To Atmosphere

H2O and

NaOH

H2O

Electrolytic Reduction

Cell

Waste Stream

Gas

Waste Stream

Scrubber

Quench

Gas Wet

Rare Earth Chloride

Drier Dry Rare Earth Chloride

To Atmosphere

H2O Waste Stream

H2O

H2O and

NaOH

To Atmosphere

Scrubber

Gas

Quench

Scrubber

Filter

Dilute NaOCl

Backwash

H2OWaste Stream

Gas

Dry Rare Earth

Mischmetal to Casting/Forming

Slag

1

2

1

3

4

5

NaOCl

Chloride

Wastewater from caustic wet air pollution control. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 100 metric tons/yr, 500,000 metric tons/yr, and 1,000,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristics of toxicity for chromium and lead and corrosivity. Scrubber liquor is recycled and the bleed stream is discharged to treatment. This waste formerly was classified as a spent material.

Spent electrolytic cell quench water and scrubber water. Waste characterization data are presented in Attachment 1. This waste is not expected to be hazardous.

Electrolytic cell caustic wet APC sludge. Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 70 metric tons/yr, 700 metric tons/yr, and 7,000 metric tons/yr, respectively. We used best engineering judgment to determine that this waste may exhibit the characteristic of corrosivity. This waste is recycled and is classified as a sludge.

Spent sodium hypochlorite filter backwash. The caustic wet air pollution control system following the water quench or water scrubber is designed to recover chlorine present in the gas stream. Sodium hydroxide is circulated through the scrubber and the reaction with chlorine forms sodium hypochlorite. When a 12 to 15 percent sodium hypochlorite concentration is attained, the solution is drawn off and sold for industrial use. This waste is not expected to be hazardous.


Ancillary hazardous wastes may be generated at on-site laboratories, and may include used chemicals and liquid samples. Other hazardous wastes may include spent solvents (e.g., petroleum naptha), and acidic tank cleaning wastes. Non-hazardous wastes may include tires from trucks and large machinery, sanitary sewage, waste oil (which may or may not be hazardous), and other lubricants. At Molycorp, Inc’s facility in Mountain Pass, CA several wastes are considered to be non-uniquely associated. These include pinion grease (contains 50 percent aromatic oils, 35 percent petroleum asphalts, and 0-10 percent 1,1,1 trichloroethane) and spilled solvent cleaned from the chemical plant’s floor.



Two commenters provided new information on facility specific operations and processes (COMM58, COMM68). This new information was incorporated into the Agency’s sector report.


Two commenters objected to EPA’s determination that mineral processing occurs in the rare earth sector, in that they believed this was a reversal of a prior determination by the Agency (COMM40, COMM58, COMM68). One commenter, Molycorp, Inc., responded to both the Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes and the Second Supplemental Proposed Rule Applying Phase IV Land Disposal Restrictions to Newly Identified Mineral Processing Wastes (COMM68, COMM40). The concerns of Molycorp, Inc. stem from the Agency determining that mineral processing occurs in the rare earth sector, rather than it being strictly a beneficiation process, which the commenter believed contradicted the 1989 Mining Waste Exclusion Rule.

BIBLIOGRAPHY

Castor, Stephen B. "Rare Earth Minerals." From Industrial Minerals and Rocks. 6th ed. Society for Mining, Metallurgy, and Exploration. 1994. pp. 827-837.

Hedrick, James. "Rare Earths." From Mineral Commodity Summaries. U.S. Bureau of Mines. 1995. pp. 134-135.

Hedrick, James. "Rare Earths, the Lanthanides, Yttrium, and Scandium." From Minerals Yearbook Volume 1. Metals and Minerals. U.S. Bureau of Mines. 1992. pp. 1035-1047.

RTI Survey, W.R. Grace, Chatanooga, TN, 1988, ID# 101824.

RTI Survey 101402. National Survey on Solid Wastes from Mineral Processing Facilities. Rhone-Poulenc, Freeport, TX. 1989.

U.S. Bureau of Mines. Rare Earths Annual Report, 1993.

U.S. Environmental Protection Agency. Molycorp Waste Interpretation, Briefing for Matthew Straus, March 6, 1992.

U.S. Environmental Protection Agency. Newly Identified Mineral Processing Waste Characterization Data Set. Office of Solid Waste. Vol. I. August 1992. pp. I-2 - I-8.

U.S. Environmental Protection Agency. Newly Identified Mineral Processing Waste Characterization Data Set. Office of Solid Waste. Vol. I. August 1992. pp. 10-2 - 10-18.

U.S. Environmental Protection Agency. Development Document for Effluent Limitations Guidelines and Standards for the Nonferrous Metals Manufacturing Point Source Category. Vol. X. Office of Water Regulations Standards. May 1989. pp. 5376-5446.

U.S. Environmental Protection Agency. Technical Background Document, Development of the Cost, Economic, and Small Business Impacts Arising from the Reinterpretation of the Bevill Exclusion for Mineral Processing Wastes. Office of Solid Waste. 1989. pp. A-21 - A-22.

U.S. Environmental Protection Agency. "Rare Earths." From 1988 Final Draft Summary Report of Mineral Industry Processing Waste. 1988. pp. 3-164 - 3-174.

ATTACHMENT 1

SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - SPENT SURFACE IMPOUNDMENT LIQUIDS - CERIUM\LANTHANIDES\RARE EARTHS




- - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

0.008 0.008 0.008 1/1 - - - 0/0 - - - 0/0 - - - 0/0

0.03 0.03 0.03 1/1 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 100.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 0.2 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 0 - -


SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - SPENT SURFACE IMPOUNDMENT SOLIDS - CERIUM\LANTHANIDES\RARE EARTHS




20000 20000 20000 1/1 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

20000 20000 20000 1/1 7500 7500 7500 1/1

- - - 0/0 2000 2000 2000 1/1

- - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

110000 110000 110000 1/1 - - - 0/0

33 33 33 1/1

- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 100.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 0.2 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 0 - -


SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - SPENT AMMONIUM NITRATE PROCESSING SOLUTION - CERIUM\LANTHANIDES\RARE EARTHS




0.046 0.38 0.97 3/3 0.229 10.11 20 2/2

0.0025 0.01 0.025 4/5 0.038 0.07 0.11 5/5 0.009 0.01 0.009 1/1

- - - 0/0 0.0025 0.03 0.095 4/5 0.009 0.06 0.24 3/5 0.054 4.93 9.8 2/2 0.005 0.04 0.085 2/3 0.053 0.05 0.053 1/1 0.001 0.02 0.03 4/4 0.005 56.08 221 6/6 0.005 0.02 0.045 3/4

0.0001 0.00 0.0005 2/3 - - - 0/0 - - - 0/0

0.0025 0.01 0.016 1/3 0.005 0.04 0.097 3/5

- - - 0/0 - - - 0/0

0.001 0.02 0.046 3/4 0.005 0.09 0.25 0/3 0.025 0.34 0.5 0/3

69 595 1,494 3/3 - - - 0/0 - - - 0/0 - - - 0/0

1,126 11,108 21,300 3/3 - - - 0/0

0.1 7.07 9.59 9/9 107.13 109.17 111.2 2/2

- - - 0/0 - -- - - 0/0 - -

0.002 0.049 0.132 3/3 5.0 0 0.006 6.99 20 3/3 100.0 0

- - - 0/0 - -- - - 0/0 - -

0.003 0.013 0.03 3/3 1.0 0 0.027 0.048 0.079 3/3 5.0 0

0.0005 0.065 0.15 2/3 - -- - - 0/0 - -- - - 0/0 - -

0.005 0.014 0.02 2/3 5.0 0 - - - 0/0 - -- - - 0/0 - -

0.0065 0.06 0.094 2/3 0.2 0 0.009 0.07 0.124 3/3 - -0.004 3.28 9.8 3/3 - -0.023 0.05 0.095 3/3 1.0 0 0.009 0.02 0.038 3/3 5.0 0

- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 1 - -


SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - PROCESS WASTEWATER - CERIUM\LANTHANIDES\RARE EARTHS




27.9 35.7 43.5 2/2 0.50 0.50 0.50 0/2 0.50 0.50 0.50 0/2 0.50 0.50 0.50 0/2 0.05 0.05 0.05 0/2

- - - 0/0 0.00050 0.039 0.054 1/4 0.00050 0.26 0.50 1/4

0.5 0.50 0.50 0/2 0.5 1.08 1.65 1/2

8.57 10.19 11.80 2/2 0.0005 2.50 8.45 3/4

154 2,117 4,080 2/2 3.68 104 204 2/2

0.00010 0.00010 0.00010 0/2 0.50 0.50 0.50 0/2

0.008 1.25 4.00 2/4 0.50 0.50 0.50 0/2 0.50 0.50 0.50 0/2 2.50 2.50 2.50 0/2 0.50 0.50 0.50 0/2 1.98 8.09 14.20 2/2

- - - 0/0 - - - 0/0

152 786 1,420 2/2 0.20 15.10 30.0 2/2

- - - 0/0 - - - 0/0

0.034 1,675 6,490 4/4 0.030 4,740 9,480 2/2

0.4 0.7475 1.1 4/4 - - - 0/0

23.2 25.6 28 2/2 - -0.50 0.50 0.50 0/2 - -0.50 0.50 0.50 0/2 5.0 0 0.50 0.85 1.20 1/2 100.0 0 0.05 0.05 0.05 0/2 - -

- - - 0/0 - -0.05 0.05 0.05 0/2 1.0 0 0.50 0.50 0.50 0/2 5.0 0 0.50 0.50 0.50 0/2 - -0.50 1.56 2.62 1/2 - -7.55 7.76 7.97 2/2 - -0.63 5.31 10.0 2/2 5.0 1

1,020 4,955 8,890 2/2 - -2.52 10.4 18.3 2/2 - -

0.0001 0.0001 0.0001 0/2 0.2 0 0.50 0.50 0.50 0/2 - -0.50 0.50 0.50 0/2 - -0.50 0.50 0.50 0/2 1.0 0 0.50 0.50 0.50 0/2 5.0 0 2.50 2.50 2.50 0/2 - -0.50 0.50 0.50 0/2 - -1.98 7.24 12.5 2/2 - -

- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 4 - -


SUMMARY OF EPA/ORD, 3007, AND RTI SAMPLING DATA - SPENT ELECTROLYTIC CELL QUENCH WATER - CERIUM\LANTHANIDES\RARE EARTHS




- - - 0/0 0.005 0.0067 0.01 3/3 0.006 0.0177 0.025 3/3

- - - 0/0 0.001 0.0010 0.001 3/3

- - - 0/0 0.001 0.0073 0.02 3/3 0.001 0.0173 0.033 3/3

- - - 0/0 0.01 0.0230 0.033 3/3

- - - 0/0 0.14 0.2733 0.4 3/3

- - - 0/0 - - - 0/0

0.0002 0.0008 0.002 3/3 - - - 0/0

0.013 0.0380 0.051 3/3 0.005 0.0110 0.023 3/3 0.001 0.0010 0.001 3/3 0.001 0.0057 0.015 3/3

- - - 0/0 0.06 0.1167 0.19 3/3

0.0003 0.0075 0.022 3/3 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0 - - - 0/0

- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 100.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 0.2 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 1.0 0 - - - 0/0 5.0 0 - - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -- - - 0/0 - -

2<pH>12 0 - -


RHENIUM


The principal source of rhenium is molybdenum concentrates which are derived from porphyry copper deposits. Rhenium-containing products include ammonium perrhenate, perhennic acid, and metal powder. Rhenium is used in high-temperature superalloys (such as those used for manufacturing jet engine components) because it improves the strength properties of nickel alloys at high temperatures (1,000 oC). Rhenium alloys are used in thermocouples, temperature controls, heating elements, ionization gauges, mass spectrographs, electron tubes and targets, electrical contacts, metallic coatings, vacuum tubes, crucibles, electromagnets, and semiconductors. Rhenium is also used in petroleum-reforming catalysts for the production of high octane hydrocarbons for use in lead-free gasoline. Bimetallic platinum-rhenium catalysts have replaced many of the monometallic catalysts.1

Rhenium is usually traded either as ammonium perrhenate or rhenium metal.2

According to the U.S. Bureau of Mines, ores containing rhenium are mined domestically by eight companies. Exhibit 1 presents the names and location of those companies generating molybdenum concentrates that contain rhenium.

EXHIBIT 1

SUMMARY OF RHENIUM FACILITIES

Facility Name Location Type of Operation

Chino Mines Co. Hurley NM Molybdenum concentrates

Cyprus-Climax Sierrita, AZ Molybdenum concentrates

Cyprus-Climax Bagdad, AZ Molybdenum concentrates

Kennecott Minerals Co. Bingham Canyon, UT Molybdenum concentrates

Magna Copper Corp. San Manuel, AZ Molybdenum concentrates

Magna Copper Co. Miami, AZ Molybdenum concentrates

Phillips Dodge Corporation Morenci, AZ Molybdenum concentrates

Sheilds Resources Inc. (Continental Pit) Butte, MT Molybdenum concentrates

Although most of these companies typically send their concentrates out of the United States to be toll refined, there is one compnay that recovers and refines rhenium domestically. Cyprus-Climax roasts and recovers rhenium at their Sierrita facility. Additionally, Cyprus-Climax has a rhenium recovery operation at Fort Madison, Iowa.3 Rhenium consumption was estimated as 6,000 kilograms in 1994.4

1 Blossom, J. W., "Rhenium," from Mineral Commodity Summaries, U.S. Bureau of Mines, 1995, pp. 136-137.

2 Blossom, J.W., "Rhenium," from Mineral Facts and Problems, 1985, p. 667.

3 Personal communication between Jocelyn Spielman, ICF Incorporated, and J.W. Blossom, U.S. Bureau of Mines, October 17, 1994.

4 Blossom, J. W., 1995, Op. Cit., p.136.



In general, rhenium is recovered from the off-gases produced when molybdenite, a byproduct of the processing of porphyry copper ores for molybdenum, is roasted. During the roasting process, molybdenite concentrates are converted to molybdic oxide and rhenium is converted to rhenium heptoxide. The rhenium oxides are sublimed and carried off with the roaster flue gas, sulfur oxides, and the entrained dust. Once the technical grade molybdic oxide is separated from the off-gases, it may be further processed to either molybdenum or ferromolybdenum.5 The off-gases are then processed to recover rhenium as described in detail below. Exhibit 2 provides an overview of the rhenium recovery process and how it is associated with the production of molybdenum.


As shown in Exhibit 3, the rhenium recovery process can be separated into five main steps: (1) scrubbing; (2) solvent extraction or ion exchange; (3) precipitation (addition of H2S and HCl) and filtration; (4) oxidation and evaporation; and (5) reduction.

Scrubbing

The rhenium heptoxide entrained in flue gas is readily soluble in aqueous ammonia solutions and can be removed by wet scrubbing. Collection efficiencies are on the order of 65% and the unrecovered rhenium remains in the off-gases that escape into the stack.6


The rhenium heptoxide absorbed and dissolved in the scrubber liquor can be recovered at much greater efficiencies than the rhenium from the flue gas. Recoveries of better than 95% have been attained from liquor with rhenium concentrations in excess of 300 ppm. The rhenium is removed from the scrubber liquor via either solvent extraction or selective ion exchange in a solid bed.7

Precipitation and Filtration

After ion exchange treatment (or solvent extraction) rhenium is stripped from the resin (or solvent) and recovered from the resulting eluviate solution as ammonium perrhenate crystals (NH4ReO4).888 As shown in Exhibit 2, the perrhenate solution is precipitated to ReS2 through the addition of H2S, HCl, and NH4CNS, followed by filtration. The resulting salt solutions are then sent to further treatment.

5 U.S. Environmental Protection Agency, Development Document for Effluent Limitation Guidelines and Standards for Nonferrous Metals Manufacturing Point Source Category, Vol. II, Office of Water Regulations Standards, May 1989, pp. 3363.

6 Ibid., p.3365.

7 Ibid.

8 Ibid.

EXHIBIT 2

MOLYBDENUM AND RHENIUM PRODUCTION PROCESSES (Adapted from: Development Document for Effluent Limitation Guidelines and Standards for Nonferrous Metals Manufacturing

Point Source Category, 1989, pp. 3341 - 3483.)

SO2 Scrubber or

Acid Plant

Gas

Wastewater

Rhenium Recovery Scrubber

Gas

Rhenium Scrubber Solution Wastewater


Molybdenum

Gas

Roasting

Technical Grade Molybdic Oxide

Leaching

Wastewater

Molybdenum Metal Powder Reduction

Furnace

Scrubber

H2 Gas

DissolvingSulfideConcentrate

Crystallization

Sublimation Pure

Molybdic Oxide

Crude Ammonium Perrhenate

Ammonium Molybdate

Leaching, Ammonium Oxide

Crystallization Molybdate

Pure Molybdic

Dissolving, Calcining

Rhenium Metal

Molybdenum Sulfide Concentrate

Purification, Reduction

Wastewater

Wastewater

EXHIBIT 3

RECOVERY OF RHENIUM FROM MOLYBDENITE CONCENTRATES


To Stack or SO2 Capture (APC Dust)

NaOH Make-Up Water,

Dust/Sludge

Scrubbing

Sludge Separation

Dust RemovalTreatment

Offgases

Slag

Roasting

Dusts to

Molybdenite Concentrate

Air

Molybdic Oxide to Processing

Ion Exchange

(Solid Bed)

NH4OH Effluent

Raffinate to Neutralization, Disposal

H2S, HCl

Perrhenate Solution

to Treatment Spent Solutions

Salt Solutions to TreatmentH2

Oxidation Neutralization

Evaporation Filtration ReS2 Precipitate

Dry

Rhenium Salts

Reduction NH4CNS

Ammonia Perrhenate to Sale

H2O2, NH4OHRhenium

Metal

Reduction

The dry ammonium perrhenate is generally reduced to high purity rhenium metal powder with purified dry hydrogen in an externally heated furnace. The hydrogen reduction is accomplished in two stages, the first at 300o to 350o C and the second at 700o to 800o C. The metal powder is then sintered into bars by compression at 45 to 50 kg per mm2, using stearic acid in either stage as a plasticizer. The bars are then rolled to sheet, strip, and foil, or swaged and drawn into rod and wire. These products are annealed at recrystallization temperature after cold working to ensure maximum ductility.9


None Identified.

4. Beneficiation/Processing Boundary

Since rhenium is recovered from off-gases from the production of molybdenum, please see the report for molybdenum presented elsewhere in this background document for a description of where the beneficiation/processing boundary occurs for this mineral commodity sector.



None Identified.


Exhibits 2 and 3 identify the following wastes associated with the recovery of rhenium.

Roasting and Wet Scrubbing

Slag. Slag is produced during roasting. Existing data and engineering judgment suggest that this material does not exhibit any characteristics of hazardous waste. Therefore, the Agency did not evaluate this material further.

Roaster Dust. Dust removed after the roasting of molybdenum concentrates is sent to further treatment. Existing data and engineering judgment suggest that this material does not exhibit any characteristics of hazardous waste. Therefore, the Agency did not evaluate this material further.

APC Dust/Sludge. After wet scrubbing, unrecovered rhenium remains in the off-gases that are captured in the stacks. The captured dust and sludge are sent to further treatment. Existing data and engineering judgment suggest that this material does not exhibit any characteristics of hazardous waste. Therefore, the Agency did not evaluate this material further.

Spent Barren Scrubber Liquor. Barren scrubber liquor generated during wet scrubbing contains treatable concentrations of toxic metals, particularly selenium. Although it is discharged as a wastewater stream, the two plants that report this waste stream achieve zero discharge. Specific practices at these two plants through lime addition and sedimentation, total reuse in other plant processes, evaporation, and contract hauling.10 Although no published information regarding waste generation rate or characteristics was found, we used the methodology outlined in Appendix A of this report to estimate a low, medium, and high annual waste generation rate of 0 metric tons/yr, 100 metric tons/yr, and 200 metric tons/yr, respectively. We used best engineering judgment to determine

9 J.W. Blossom, 1985, Op. Cit., p. 667.

10 U.S. Environmental Protection Agency, 1989. Op. Cit. p. 3430

that this waste may be recycled and may exhibit the characteristic of toxicity for selenium. This waste was formerly classified as a spent material.

Ion Exchange and Solvent Extraction

Spent Rhenium Raffinate. As shown in Exhibit 3, raffinate results from the solid bed ion exchange and is sent for neutralization and disposal. This waste stream has a reported waste generation rate of 88 metric tons/yr. We used best engineering judgment to determine that this waste may exhibit the characteristic of toxicity for lead.

Spent Ion Exchange Solutions. Two facilities reporting this waste stream from ion exchange achieve zero discharge through treatment, reuse, evaporation ponds, and contract hauling. Although no analytical data are available for this waste stream, one facility reported that the solution contains treatable concentrations of selenium as well as high concentrations of molybdenum and iron. When rhenium recovery is achieved using solvent extraction, the resultant solution may also contain priority organics.11 Existing data and engineering judgment suggest that this material does not exhibit any characteristics of hazardous waste. Therefore, the Agency did not evaluate this material further.

Precipitation and Filtration

Spent Salt Solutions. The salt solutions that result from filtration are sent to further treatment. Existing data and engineering judgment suggest that this material does not exhibit any characteristics of hazardous waste. Therefore, the Agency did not evaluate this material further.


Non-uniquely associated and ancillary hazardous wastes may be generated at on-site laboratories, and may include used chemicals and liquid samples. Other hazardous wastes may include spent solvents, and acidic tank cleaning wastes. Non-hazardous wastes may include tires from trucks and large machinery, sanitary sewage, and waste oil and other lubricants.


EPA received no comments that address this specific sector.

11 U.S. Environmental Protection Agency, 1989. Op. Cit. p. 3381

BIBLIOGRAPHY

Blossom, J.W. "Rhenium." Mineral Commoditity Summaries. 1995. pp. 136-137.

Blossom, J.W. "Rhenium." From Mineral Facts and Problems. U.S. Bureau of Mines. 1985. pp. 666-667.

Personal communication between Jocelyn Spielman, ICF Incorporated, and J.W. Blossom, U.S. Bureau of Mines. October 17, 1994.

U.S. Environmental Protection Agency. Development Document for Effluent Limitation Guidelines and Standards for Nonferrous Metals Manufacturing Point Source Category. Office of Water Regulations Standards. May 1989. pp. 3341-3483.

U.S. Environmental Protection Agency. "Rhenium." From 1988 Final Draft Summary Report of Mineral Industry Processing Wastes. Office of Solid Waste. 1988. pp. 3-175 - 3-178.

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